Welcome to my second build. This time, the incredible tank, Maokai (I Am Oak). First thing's first, Maokai is most effective in the lane, with a partner, specificially one who casts many spells. I do not believe in Maokai's purpose being a jungler, although he can definitely fit that role. As with my Anivia builds, I'm not intending to make a tried and true, ultimate, competitive build. I'm a pretty casual LoL player, as far as League players go. I play somewhere between tanky AP and a pure tank. I've played Maokai since season 2, and tried numerous builds with him. One final note, it's important to realize that Maokai's main job is not to take the feed, but to protect the team, and get them fed whenever possible. I've tried playing him as a pure tank, but he falls off late game, and I don't find it to be worth it. Without a taunt, Maokai's difficult to be played as a pure tank. The good news is that he hurts pretty bad for someone so tanky (although, less tanky now in Season 3). I appreciate constructive criticism, however, don't waste your time commenting if all you're going to do is complain about how I'm not following the meta, or something equally pointless.

OP: Overpowered
AD: Attack Damage
AP: Ability Power
MS: Movement Speed
MR: Magic Resist, magic defense
CDs: Cooldowns
CDR: Cooldown Reduction
AoE: Area of Effect
SS: Summoner Spell
HP: Hit points; health, life
MP: Magic points; mana
CC: Crowd control. League has a bizarre usage of this term. It doesn't mean dealing with a group of enemies, like in everything else. CC in League of Legends is equivalent to status effects (ex. poison, darkness, slow, etc.) in anything else.

RoA: Rod of Ages
MFSB: Moonflair Spellblade
Abyssal: Abyssal Mask
Iceborn/IBG: Iceborn Gauntlet
Torment: Liandry's Torment
Rylai's: Rylai's Crystal Scepter
Warmog's: Warmog's Armor
Unholy: Athene's Unholy Grail
Witchcap: Wooglet's Witchcap
FH: Frozen Heart

Vile: Vilemaw

TT: Twisted Treeline
SR: Summoner's Rift
3s: 3vs3; Twisted Treeline
5s: 5vs5; Summoner's Rift
Old 3s: TT prior to the total remodel on 10-25-12.
New 3s: The current TT, with Vilemaw, new items, etc.
"Glass": Little to no defense. Mages can probably kill you in one or two bursts.

IMO: In my opinion
ATM: At the moment

If there's anything I missed, please let me know.

Maokai's a very unique, tanky AP champ. He gets incredibly tanky for how strong he is, although, he definitely doesn't have carry damage potential. He's more about CC, providing both offensive and defensive opportunities for your team. He shouldn't just be chosen as a tank, he needs the right type of team in order to excel. As a tanky AP champ, Maokai's gotten nerfed pretty hard in the transition from season 2 to season 3. Not only does he not benefit from magic pen, but since armor/magic pen got buffed, it's harder for him to tank as effectively. Regardless, Maokai's still a contender.

Strengths
One of the best harrassing abilities in the game: Sapling Toss (also acts as built-in wards, is excellent for zoning, and can be thrown further than their max range if you toss them onto terrain/walls)
Very durable, boasting the highest natural armor in the game (tied with Poppy), and various methods of staying alive
Very strong for a tanky AP champ (can't blow squishies up anymore, but all of the other changes are a buff)
His W, Twisted Advance, can counter Flash (less often with the range reduction, but still), and set his team up for some easy kills
Excellent CC
Excellent pusher, especially against caster minions ( Sapling Toss)
Unreasonably good ganking potential, which almost always result in a kill with the right team, and proper timing
Pretty fast with this build, which makes his jobs easier, and harder to ignore
Can get most enemies off of your teammates with moderate ease
Can easily interrupt quite a few skills (especially channeled ones, ex. Katarina's Death Lotus, Nunu & Willump's Absolute Zero, Fiddlesticks' Bountiful Harvest, Master Yi's Meditate, etc.) (via his Q, Arcane Smash)
Decently flexible, can get damage or tankiness depending on what he needs (high AP ratios, high natural armor, healing passive. He's rewarded for being strong and tanky, not just one)
Good pick for jungle or duo bot

Weaknesses
No scaling MR
No level 6 power spike
Cannot demand focus like other tanks, such as Rammus and Shen
Mana hungry at all points of the game
Almost no physical damage: weak, realatively slow basic attacks
Needs a lot of different stats to get to his full potential (as opposed to most mages, for example, who only need an item or two, then everything else is just extra damage): HP, MP, MS, armor, MR, CDR, Tenacity, AP

As previously mentioned, I tend to play Maokai tanky AP. I think that he fails to live up to his full potential as a pure mage or pure tank. A pure mage sacrificing much needed defense for a melee initiator, and a pure tank without a taunt is fairly easily ignored, plus you miss out on his high AP ratios on his spells. I take mostly defensive runes. As a tank, your main goal is to protect the team. Once (or rather, if) you have a full build, you want the turrets to tickle. You should be able to tank them without many minions, and allow your team to crush the towers without having to worry about taking damage. Maokai is tied (with Poppy) for having the highest natural armor of any champ in League of Legends. Between this fact, and his passive, he's set up to be one hell of a tank. For his runes, I recommend getting as much defense as possible, while getting just the right amount (I mean it, these quints can easily mean the difference between a kill/assist) of extra movement speed (MS) on the side. You wanna be able to catch the target with your W, Twisted Advance, which can lead to some truly EPIC ensnares. If you do, your team has a golden opportunity to eat the victim alive.

Acceptable Marks
Greater Mark of Armor: Even though Maokai has the highest natural armor in the game (tied with Poppy), extra armor can't hurt. Especially since as the tank, you're goal is to try and take all of the damage that you can. This makes doing that easier. These're my favorite marks in the game, and since you don't need magic pen, you can safely get these.
Greater Mark of Scaling Magic Resist: These're fairly weak, but they help with Maokai's lack of natural scaling MR, and when combined with Greater Glyph of Scaling Magic Resist, they stack up pretty well.

Acceptable Seals
Greater Seal of Scaling Armor: I've been trying these out, and I think that I prefer them on Maokai. He has naturally high armor, and I have armor in numerous other places in my build. This sacrifices a little early game defense for some more tankiness later on.
Greater Seal of Armor: I wouldn't take these, especially if you take Greater Mark of Armor. The scaling seals match the flats at level 6, which doesn't take long to achieve, then become three times stronger by the end of the game. When combined with Maokai's naturally amazing armor, I can't recommend these.

Acceptable Glyphs
Greater Glyph of Scaling Magic Resist: Just flat out the best glpyhs in the game, especially for a tank, and even moreso for a jungler. I recommend these for literally every 3s champ besides melee ADCs ( Yasuo, for example needs early stats).
Greater Glyph of Magic Resist: You could use these to counteract Maokai's low base MR, but I don't recommend it.

Acceptable Quints
Greater Quintessence of Movement Speed: These're extremely strong and underrated, especially on TT. MS is crucial on this map. I even take these on Anivia, they're that good.
Greater Quintessence of Armor: If all you really care about is being an unstoppable wall, these would work, I suppose. They're powerful and give you more tank stats, but you already have a lot of natural armor from other sources.
Greater Quintessence of Magic Resist: Help with Maokai's low base MR, as well as being a better tank, but I vastly prefer the MS.

Wanderer : MS is the most underrated stat in League. Unfortunately, it's out of combat only, but it's still nice.

Runic Affinity : Helps with the Smite bonuses a lot more than three enhanced potions.

Meditation : This is actually one of the more powerful masteries, so it's really nice that everyone has access to it now!

Bandit : Dangerous Game is hardly ever noticeable. I'd almost always rather have 20-40 extra gold per fight, but it's a matter of preference. Neither is amazing.

Unyielding : So much better than Recovery ! This is actually pretty powerful, especially for a tier 1 mastery.

Tough Skin : Explorer doesn't help very much on this map, as the only two frequently used bushes are in the middle, and are small. This is a guaranteed benefit to your early game jungling.

Veteran's Scars : Very solid, consistent bonus. Runic Armor would help with your passive and your high HP regen, but I feel like this is better for someone who'll be getting so much HP.

Perseverance : No contest, this is incredible compared to the alternative.

Swiftness : We're finally to the point where you have meaningful choices! I prefer this by a lot, but Legendary Guardian is also very powerful. This one's up to you, but keep in mind that Tenacity is a much harder stat to come by than armor and/or MR.

Strength of the Ages could be replaced with Bond of Stone , but the latter's weak alone, and you can still be an effective tank without directly absorbing damage for your allies. This goes well with Juggernaut and RoA's HP scaling, and once it's maxed out, it'll keep you around longer during sieging.

Philosophy
The basic mindset with Maokai is that you're a tank with the capacity to deal damage. You don't need to be a pure tank like Rammus, but you should also be very durable. It's a lot easier than it sounds. Basically, all of your items should bolster your defense. Even your items for damage should still include some form(s) of defense.

What makes an item offensive or defensive on a certain champion is based on that champion's role. Sunfire Aegis, for example, looks like a defensive item, but because of its passive and the fact that it gives lower stats than its Randuin's Omen counterpart, it's actually an offensive option for most people who would consider getting it.

Check Moonflair Spellblade out. It gives 50 AP, 50 armor, 50 MR, and tenacity. The fact that it gives you three defensive stats makes it look like a defensive item, but Maokai is a tank, so all of his items should give him at least one of the defensive stats: HP, armor, or MR. For this reason, it's actually an offensive option for him, despite the fact that it'd be a defensive item for a mage, such as Anivia or Brand. To them, they're sacrificing some AP for the defensive stats, while Maokai's sacrificing HP for some AP. Again, it's a matter of perspective.

Actual Items
Your initial items are simply to help you survive the first round of the jungle. You'll need every single item in order to live through the jungle, and at least two/three passive procs. With Cloth Armor, Greater Mark of Armor, and Hardiness , you start the game with 60 armor. You're also Maokai, who has the best natural armor in the game (tied with Poppy), and have Greater Seal of Scaling Armor, so you have a lot of armor even without items.

My usual order is Ranger's Trailblazer - Cinderhulk --> Rod of Ages --> Moonflair Spellblade, with at least Boots somewhere in between. This assumes that the game is fairly even. You'll ALWAYS be concerned with HP, MP ( Rod of Ages), armor, and magic defense ( Moonflair Spellblade). In the early game, I get AP to be more relevant, and have a function aside from initiating fights/peeling (depending on the flow of the game). I don't care too much about CDR at this point, because my mana pool is low, and most fights don't require more than two rotations of spells. At this point in the game, your spells have to mean more per cast, so damage trumps frequency.

As the game progresses, your role as a tank becomes more rigid. You have to be able to dive into a group of three enemies (with your team, obviously), and be able to stick around. It doesn't matter if your combo deals 500 more damage if you die immediately after executing it. At this point, you need CDR more than AP. It just so happens that the two best defensive items for Maokai give him a combined 30% CDR, as well as a ton of armor (100), a decent chunk of HP (which goes even further thanks to Cinderhulk), and MR, among other things.

Finishing Up
Enemy team is mostly physical damage, but includes magic: Frozen Heart --> Spirit Visage
Enemy team is mostly magical damage, but includes physical: Spirit Visage --> Frozen Heart
Enemy team is almost entirely magical damage, includes negligible physical damage: Spirit Visage --> Abyssal Mask
Enemy team is almost entirely physical damage, includes negligible magical damage: Frozen Heart --> Iceborn Gauntlet

Frozen Heart is one of the best tank items in the game, since it gives you a massive boost to defense, and increases your ability and incentive to stick around in a fight, in the forms of MP, CDR, and the aura. Without CDR and MP, you start a fight, then just kind of run around without dealing any real damage or inflicting any serious status effects to enemies. Hell, you can barely even peel.

Spirit Visage is your best bet for magic defense. It provides HP, MR, and increases your healing (this includes your passive, Sap Magic). It also gives you that crucial CDR that the tree craves. It's a very good item, but it's also fairly straightforward, so there isn't a lot to explain here. Is good. Get.

When a team consists of too much of one type of damage, you punish them on two fronts. First of all, it makes it incredibly easy to itemize against, you just get a ton of the appropriate defense. The second thing is that there're good tanky AP items that give you a reduced amount of AP while still providing solid defense.

Abyssal Mask: This is one of the best items in the game. Ironically, it's rare that you can ever get it! At least on its intended audience. It's actually much better on mages, many of whom can't take full advantage of the aura, but that's a discussion for another time). It's very cheap, and gives great stats. For this reason, it's your best bet if you need a second (third? Not counting MFSB) magic defense item.

Iceborn Gauntlet: Covers the loss of CDR from skipping Spirit Visage, as well as gives a lot of armor and even more MP. It also gives you a tiny bit of damage, and giving you even more CC in the form of a slowing field. Sadly, it's expensive, and Frozen Heart is generally a better version of this (unless you focus on the Sheen aspect, like Skarner does), and for less money. It's still a good item, but as a tank, you benefit more from its big brother. That being said, if you're up against a lot of physical damage (and not much magical), get both!

Your standard, offensive combo is Sapling Toss on top of your victim, Twisted Advance the same person before the sapling lands on them, forcing them to take the first hit of the sapling. Once you arrive at the enemy, run slightly past them, and Arcane Smash them back to your team, which usually allows for the sapling to explode on them.

Upon inspection of Maokai's AP ratios, you'll notice that a little bit of AP gives Maokai a decent spike in his damage. On the flip side, a lot of AP doesn't really bring the level of power that you might expect, so don't worry too much about it on Maokai.

Start with wolves for the Thornmail-esque Smite bonus. This helps tanks more than Gift of Heavy Hands. Use your first potion after you clear this camp, as you move onto wraiths next. Use your second charge of Smite here for the heal. Use both of your remaining potions as you go to golems. Think about ganking. The third potion should keep you health enough for a gank if you decide to try one. If lanes aren't in a good spot to gank, get ready to capture an altar. A good strategy is to hit recall while standing on the altar, waiting for the first two lights of the circle to light up prior to hitting B.

Maokai is an incredible, versatile tank. He becomes incredibly difficult to kill late game, while making it very easy for your team to devour enemies thanks to his Twisted Advance. For such a durable tank, he also hurts quite a bit. While he could never carry, that isn't his job. He gets good without stealing the feed, but instead, provides it for his team.

I frequently update my guides, so expect periodic changes.