Sunfire Aegis

This item is the main item for Ornn, Often times into teams or opponents with AD damage you'll build this item. As a first item it helps with clear and deals a damage which is what you want from a first item on Ornn jungle. There is however an alternative.

Hollow Radiance

Hollow Radiance is another option for Ornn's first item, It functions almost exactly as Sunfire Aegis except that instead of increased AOE damage around Ornn it causes a small explotion around any target killed by Ornn. This item you would mainly want to go if the Enemy team is majority AP damage. Usually however Aegis is what should be built first item.

Warmog's Armor

This items synergizes well with your kit. It allows you to not have to back ever allowing crazy amounts of map pressure. With Living Forge passive that gives 10% HP or just building your first item like Sunfire Aegis or Hollow Radiance you are guaranteed to get the 1.3k bonus HP by the time you full buy it secodn item, especially if you have Overgrowth. Buying this item second will allow you to upgrade it getting a lot of raw HP (375hp). This is really good unless the enemy has a lot of % hp damage.

Heartsteel

This item isn't very reccomended if you want to teamfight, it does a load of damage and if you were the carry for your team it could work however often times it's better to go a Bami's Cinder item first for clear.

Thornmail

This item is good into AD comps that heal a lot like Olaf or Darius and into team comps that auto attack alot such as Jinx or Twisted Fate If you need MR you can buy Bramble Vest and sit on it for some time since its passive still gives grievous wounds. If the enemy team has a lot of AD damage this makes a great second item as it also gives a lot of raw stats great for tanking when upgraded(+25 Armor +185hp).

Dead Man's Plate

This allows for more MS out of combat and allows for better map pressure. The stats on thsi item are also very useful, (+25 Armor +185hp)

Randuin's Omen

Good into a fed crit ADC or comps that have a lot of crit like Tryndamere or Jinx. Watch out because some crit champs build Rageknife or Guinsoo's Rageblade and no longer deal crit dmg, then it is usually best to build Frozen Heart or Thornmail. This item is also phenomenal to upgrade as it gives the same stats as Thornmail (+25 Armor +185hp)

Frozen Heart

Good into attack speed champions like Irelia or Jax or champions that build Rageknife or Guinsoo's Rageblade.

Kaenic Rookern

Great MR item to buy second if the enemy team has a lot of MR. The magic shield and the raw stats makes it great item to upgrade(27 MR 185hp).

Abyssal Mask

MR item with good synergy with Ornns kit if you have any AP on your team or want to reduce enemy MR. When in the middle of an entire team you will gain a lot of MR along with reducing the enemies maming it a great teamfight item against MR stacking teams.

Force of Nature

MR item that gives some speed so Ornn can be more nimble in fights. The base stats give good resistances and the passive gives more MR for taking ability DMG. It feels kinda like new Adaptive Helm but with movement speed.

Spirit Visage

Don't build this item unless you have multiple enchanters on your team that will heal or shield you or if you have Sterak's Gage, Gargoyle Stoneplate or supportive ietems like Knights Vow or Redemption.

Sterak's Gage

Good item if you need damage and gives you some crazy shielding and healing in teamfights. Though usually you should go Gargoyles.

Fimbulwinter/ Winter's Approach

This item really isn't optimal only because of it's setup. You need to waste money on an early tear and the item itself isn't worth it on Ornn since it doesn't even give resistances.

Zeke's Convergence

This item lets you play around a carry better allowing you to amplify the damage of an ADC for example.

Knight's Vow

If your carry is getting killed too much, Knight's Vow lets you take some of the damage for them. Don't worry you're tanky enough.

Redemption

Lets you be a little tankier and lets you have a huge AOE heal that can be very useful in teamfights.

Mikael's Blessing

Buy this item if they have a serious form of CC that can catch a carry off guard before or during a teamfight like Enchanted Crystal Arrow or Thundering Smash. If they won't buy QSS you'll buy it for them.

CONCLUSION

In all when you are choosing what items to buy you need to look at the game at hand and when choosing what item to upgrade you want to get your golds worth. I they have a fed Yasuo or Irelia consider buying Frozen Heart. If you have a fed Yasuo or Irelia try getting Knight's Vow or Zeke's Convergence to help them out. If Syndra keeps one shotting you try Kaenic Rookern. This rule applies to any tank and is the make or break on whether you survive teamfights long enough to win them.

KEYSTONES

Phase Rush

This rune is now one of Ornn jungle's only viable rune, with inspiration tree being changed to no longer have useful secondary runes for jungle. With that and Aftershock not synergistic with Ornn, Phase Rush is the strongest option for Ornn jungle, Giving mobility for ganks and teamfights it isn't a bad choice.

Aftershock

This rune is an easier use since every ability Ornn has the ability to proc this. This is good and bad since it will be used in a fight but may be used in a bad situation like if someone stands on your Volcanic Rupture poke or when you R to engage. However the pre level 6 is better than Unsealed Spellbook since the armor and magic resist you get from this will provide skirmishing power before 6 minutes

Unsealed Spellbook

This rune is more difficult to learn than most others but it is worth it. This summoner spell you get allows you to have more utility in team fights. This rune doesn't have very good utility early since you have a useless rune until 6 minutes. If you know you will have a very passive enemy jungler who you won't 1v1 or interact with early this rune can be very good.

Glacial Augment

This rune with its rework is good on Ornn it gives good utility with all his CC along with extending his CC to massive slow AOE along with giving a keystone that has utility no matter what compared to his alternatives like Unsealed Spellbook whoch is useless for 6 minutes and Aftershock which has a chance to proc when you're nowhere near the enemy. This however is not usually the best to go since inspiration tree's rework makes it almost useless on Ornn jungle.

INSPIRATION RUNES

Magical Footwear

This rune lets you have free 300g through boots and free 10 movement speed. This is good since its free gold but also somewhat bad since you don't have boots for a while.

Hextech Flashtraption

This rune is good if you want better ganks but doesn't work too well with Unsealed Spellbook and usually isn't worth it.

Cosmic Insight

This rune is pretty good on Ornn decreases Summoner spell Cooldowns and item cooldowns. This rune is worse since the changes in preseason but is still worth picking up.

Approach Velocity

This rune is fine for Ornn since it lets him chase down targets with his Volcanic Rupture better and have more mobility with teams with CC.

RESOLVE RUNES

Font of Life

This rune is pretty good on Ornn in teamfights since every ability he has can count as CC, but isn't as good as the other Conditioning or Overgrowth to go secondary runes.

Conditioning

This allows Ornn to be more tankier into the lategame and since early game you are primarily ganking and farming it is usually better to go than Bone Plating. Conditioning lets you be tankier in teamfights and works well with Living Forge armor passive.

Bone Plating

Only go this if you NEED early game tankiness. Maybe into an early game assassin jungler that you need to 1v1. Other than that Conditioning is better.

Overgrowth

This rune goes well with Ornn letting him stack HP which increases with Living Forge passive HP increase which can help you stack a whole lot of HP making you tankier.

Unflinching

This rune goes is good into high cc comps and or high slow comps since it gives free resistances when CCd . If the enemy team doesn't have much CC or many slows then it is usually better to go Overgrowth.

Domination Runes

Cheap Shot

This rune synergizes well with Ornn since he has CC on every ability making it easy to proc off cooldown. Often times with this rune you will be doing 1k+ true damage and can help with early game skirmishing if needed.

Zombie Ward

This rune has a lot of utility, but in lower ranks the enemy warding can be unreliable and the bonus adaptive damage doesn't help Ornn that much becasue of Ornn's bad damage scaling on his abilities. Aside from that the extra utility of Zombie Ward is really worth it if you can play around it well.

Relentless Hunter

The movement speed of Relentless allows for faster responses to ganks and faster gank positioning. It got nerfed but is still a good rune for any jungler.

Ultimate Hunter

With Ornn's high cooldwon on his R Ultimate Hunter allows you to use his Call of the Forge God more and therefore make more plays. It doesn't give the movement speed of Relentless Hunter which helps Ornn, since he lacks MS, but is still a very good rune to take.

SORCERY RUNES

Nimbus Cloak

If you want movement speed in battle this helps a lot since you will have Smite Flash and a Summoner Spell from Unsealed Spellbook to have in a fight. This lets you move around a teamfight more effectively.

Transcendence

This gives Ornn Ability Haste which he likes and shred 20% of remaining cooldowns past lvl 11 allowing you to spam more abilities in a fight. This can allow you to use Searing Charge many times or get off another Bellows Breath

Waterwalking

This helps with any jungler since it improves river skirmishes and allows you to roam the map faster, two things that a jungler really wants.

CONCLUSION

In all you can shape your runes to your play style. Ornn jungle isn't the most popular thing so don't be afraid to experiment with what runes you go.

Ornn jungle is a quite off-meta pick. His ganks aren't too good and his early game skirmishing isn't antyhing to brag about so why play Ornn?

Ornn jungle has a decent enough clear to get by and scales quite well into teamfighting like most tank junglers. His passive allows him to get tanky and support his team past level 13. Ornn's passive Living Forge Also allows some map pressure most other junglers can't reproduce since he doesn't need to back often. Ornn definitively isn't the best jungler out there and really isn't a good blind pick but he is a really fun tank jungler that brings a totally unique and refreshing playstyle to your game.