Hello all! I'm not any pro with Warwick, but before you wanna stop reading, think again. I have used this build a lot and this is a pretty stong one. However the problem is that you are kinda squishy then. Build this only if your team has enough tankyness and cc. First you can try it off a normal to actually see how it works out for you. Note that his build is mostly at fun for the first time, however there actually are situations where this build can do really well.

I take 9x Greater Mark of Attack Damage and 3x Greater Quintessence of Attack Damage to have a nice amount of Attack Damage from early on. It's easy to clear in early camps in early game.

I use 9x Greater Seal of Scaling Health to have more hp + it makes use out of masteries. Also the 9x Greater Glyph of Armor is nice, because it defends you a bit in the jungle and you'll do better against AD carrys and such. You can replace the armor runes with something else if you find want to.

I usually go 21/9/0 with masteries. As said you can actually get some Utility points if you want, to have a greater movement speed.

Offense Tree:
Double-Edged Sword gives some nice damage output and Butcher helps you with camps. Fury and Frenzy synergize well with Warwick's Hunters Call(W).
Claw Weav... emh I meant Blade Weaving :P. It's great because Warwick usually enters a fight with his abilities first, and if these aren't enough he uses his basic attacks to finish his enemy off.
Executioner is also a nice Mastery. Warwick has a great damage potential and Warwick's Blood Scent(E) gives him movement speed when his enemies have low health. It works extremely well with Executioner .
Martial Mastery and Warlord masteries. Well duh? Warwick is primarly a fighter and he needs Attack Damage. No Question!
I get two points on Devastating Strikes to have Armor and Magic penetration. Arpen works great with Basic attacks and Magic penetration helps with your onhit Magical Damages. I have to sacrifice one point because Warwick goes good with both Double-Edged Sword and Butcher . This sacrifice will only do good.
Finally a point of Havoc is good to increase your damage output.

Defense Tree:
Tough Skin will again help your jungling.
Recovery points are nice too, you'll generate health even faster!
Bladed Armor . Again, something for early jungling potential.
Veteran Scars is just a nice resource of health which also Synergizes with Juggernaut I pick Juggernaut to be a bit more tankier, because with this build you aren't very tanky and extra point on Juggernaut is no harm :)

Utility Tree:
I usually don't get any points here, however if you'd like to have some, then get some!
Use your senses here. Do you want 9 points from Utility? Maybe you want to mix Utilty and Defense. Well if I had to pick from utility, then I'd pick Fleet of Foot so I could chase better even if the target isnt low health.
Expanded Mind won't be as bad either. Warwick has a pretty bad mana pool and these bonus mana points kinda help you to land one more Hungering Strike(Q) or some other ability when you don't have a blue buff.

Jungle items at the beginning should be quite obvious. Hp pots x2, a warding totem and the Machete for the base of your Smite upgrade.
I'd recommend the Skirmisher's Sabre to make you burst enemies down even faster. The true damage is a real pain ontop of the Magic damage and Physic damage that you offer.
Ranger's Trailblazer is kinda meh. You can clear camps without getting damaged too much and you don't really need it. Stick with the Skirmisher's Sabre.
At first back you also should buy a Stealth Ward to safely kill a Dragon early.
I usually take the [Boots of Lucidity so I could use Q more often and have a non existant ultimate cooldown in lategame. Other nice choices are Boots of Mobility for an unreal movement speed to initiate. Mercury's Treads and Ninja Tabi are nice because of it's tenacity and defensive stats.
Your core items are: Skirmisher's Sabre - Devourer , Wit's End and Blade of the Ruined King . These items combined give a crazy onhit damage and synergize well with the Devourer enchantment, especially when it's fully stacked. Blade of the Ruined King itself is nice to get rid of targets with high health.
I upgrade boots with the Enchantment:Captain or Enchantment:Homeguard . The first option when we you are winning, and the second option when you are losing.
I finalize my build with 2 tank items, because you already do great damage and building more damage would be good, only if you somehow could get close without dying. So get tank items instead. There are multiply options to choose from depending on your enemy team.

: This is the core of Warwick. Inbuilt sustain which increases on hits and gives magical damage ontop of your basic attacks. Comes clawy.. dammit handy I meant... handy in the jungle

: A nice ability which also gives Warwick inbuilt sustain. Deals a good amount damage with %health which is really great. It's also magic damage! Can be used in fights, for chasing and more. Really cl... handy in the jungle also! Can be used after using your Infinite Duress to finish your enemy off.

: A really nice ability which lasts quite long and gives attack speed to your allies and you. Use it in the jungle, in teamfights, while turretpushing and such.

: Helps you find low health enemies and gives you a movement speed buff when detecting a low health target.
Tip: When you see a low health enemy from so far that your Blood Scent hasn't detected it yet, then toggle your Blood Scent off. The enemy won't know you are around and you can make a surprise for him/her. When she/he is getting away then just toggle your [blood scent back on.

: A great sustain lockon ability. Use it when you see a solo enemy. Use it in teamfights after your enemies blew their cc off. This ability deals pretty good damage and also heals you. Be smart when using it, and you'll win fights.

I start with Hunters Call(W) so I gain attack speed with an ally(ies) who help me at my first camp( Gromp ). Obviously the attack speed for a long duration makes you deal more damage than one Hungering Strike.
Secondly I put a point on Hungering Strike so I can heal myself and deal more damage. I level this ability twice on level 2 and 3. It's needed to get the Dragon down early on(great healing from the Hungering Strike )
Later on level 4 Get a point on Blood Scent(E). Then start maxing Q and W repeadetly and max your Infinite Duress(R) whenever it's possible to. I don't max one ability staright because both Hungering Strike(Q) and Hunters Call(W) both give really useful stats.

I choose Flash because it's a really flexible summoner spell for both disengaging and engaging. For example you can flash closer to your enemy team and instantly ult someone, locking the enemy down so your team could blast the other teammates down. Doesn't matter if the whole enemy team starts focusing you at the given time, you'll still kill the squishy target if your team follows up fast.(Be aware that the enemy team can't cc you)
I choose Smite because well... Isn't it a Summoner Spell which every jungler should use?

Ranked is the serious play. In ranked you build this way only if...
1)Your team has enough tankiness and crowd control.
2)You know how to play with this build
3)You know how to use Warwick
Otherwise you can screw up very hard.

Pros + High damage + Good in-built sustain(Solo Baron Nashor and Dragon) + Attack and Movement speed Steroids + A great lockdown ultimate + A great duelist + Scales well into lategame + Is a f*cking werewolf!

Cons - Lacks CC - Not the best early game - Small mana pool - Ultimate can be interrupted - Can only be played when it's full moon(otherwise turns back into a human)

While jungling, take the Gromp with a smite and don'tuse a single Health Potion before I have written so.. Then get the Blue and then the Wolves. Then go for the Red and again no smite. Now back and you have money to buy an upgraded smite and a Stealth Ward. Go to Drake and ward with your Stealth Ward and Stealth Ward. Use one smite immidiately(you should have 2 Smites ) and the second one when Drake has low health so you could smite(Use your Health Potions right after using your 1st Smite ). Continue taking a Dragon every time he respwans when it's possible(Ward!) Doing this should get you 5 dragons in around 30 minutes.

Let your tank(s) initiate and then go with your team and ultimate their carry. However let enemy team blast off their main cc abilities first, so your ultimate might not get interrupted. When an enemy AD carry has got a Quicksilver Sash, then I'd recommending ulting their mage unless you are 100% sure that their AD carry has the Quicksilver Sash on cooldown. When you survive after the ultimate ends, finish the target you ulted off when she/he isn't deat yet. When still alive then take on other weak targets.

If you actually did read all this, then thank you a lot for reading my Warwick guide! This is my first guide and I'm not very good at making guides and designing the colomns and such(obvious). I hope you'll have fun with this build ;)