So a while ago I realized that Garen had the potential to become a really excellent jungler, in fact I think his best role. Apparently there was a patch modification to judgement that really increased its power against monsters. Everyone knows hes the classic bush lurker and jungling just puts him in his truly native environment. I main jungle Jarvan and realized his biggest problems were aggressive duelist counter junglers and being banned. I'm grooming Garen as his stand-in.

Alot of people view Garen as a potential tank. He really isn't. Fully tanked up he lacks cc and enough damage to force people to take notice of him. Fully glass cannon'd and he's meat for the mill. So, he really has but one job and its offtank. If you choose him you must ensure your team has at least another offtank, and perhaps preferably a main tank. I've left a few optional items to allow some variance in the build depending on your team's tanking vs. damage needs.

Pros: fast clears, strong duelist, good ganks, massive aoe damage, rapid exp/item/gold gain, solid performance throughout game
Cons: lacks cc, may have difficulty against opponents stacking armor

I hope these are all non-controversial choices. It seems utterly clear to me that any tank/offtank should be in the defensive tree. It gives way too much yummy goodness to ignore.

Skillwise judgement provides absolutely awesome damage and is a must for quick jungle clearing and is thus ranked first. Decisive strike helps with ganks, moving between camps, and is ranked second. Courage should not be ranked until you have some defensive items that benefit from its passive, or unless you really feel you need the cc reduction. The final ranks are obtained last while your ultimate is of course ranked as quickly as possible.

This build runes give about 12 base arpen and 7 ad. I think this is the right ratio since creeps and monsters are all like 12 armor, thus giving true damage against them.

Smite: is obviously for jungling.
Ghost: I continue to like ghost despite the fact garen doesn't have a wall jumping move. Its just so utterly useful, especially in terms of sticking to opponents, executing decisive ganks, and saving towers under heavy pressure, and quite frankly I think its the superior escape mechanism. It just lasts so blithering long you can cover way more ground than you can with flash.

After much thinking I am nearly sure that wriggle's is the way to go, as well as a lifesteal item. You end up dropping a key item from the final build, and I chose the arpen item. Lifesteal, wriggle's, and mobility boots make an amazing jungling combo that may give the fastest clears in the game. The key to this build is ridiculous fast jungling, fast exp, rapid gold generation, and hard decisive ganks. With mobility boots, his Q, and perhaps ghost, garen can close ridiculously fast on his ganks. This is an extreme advantage and has lead me to want to build mobility boots if at all possible for every jungler.

There is a lot you could say about his passive. If you are going cross map you can definitely gain some benefit from it and with mobility boots you have absolutely superb long gank potential. I think too that in the very early game its probably going to be necessary to just sit and do nothing for a bit in order to keep your health at safe levels, camping top lane a can do that for you.

In a pure top lane alot of people think that his passive turns garen into the immovable rock of toplane dominance. Well he is against tankish/short range types. But heavy harass champs can eat him for breakfast. You might succeed with heavy bush lurking, but i really consider him a tank/bruiser counterpick.

Mobility Boots vs. Others: The more I play the more I like mobility boots. They are just perfect for junglers, ganking, moving between camps, getting out of base, chasing people down. I've gotten to level 18 and been 2...maybe 3 levels ahead of my competing jungler. I would consider getting ninja tabi or merc treads if i'm overly concerned about hard counterjungling, but frankly garen has a very strong early game and this seems unlikely.

Vampiric Sceptre, Bloodthirster: I like lifesteal on garen, once you get it your health pretty much stays maxxed during jungling, it improves tankiness during duels and fights, and the massive ad contribution from BT is extremely yummy.

Gold Items: Avarice blade and Wriggle's Lantern work extremely well on Garen and significantly contribute to his mid/late game dominance. They both pay for themselves well and Wriggle's can be sold at high value (replaced by Phantom Dancer), while Avarice blade gets built into Atma's.

Critical strike: Critical strike is GOOD on Garen. Both decisive strike and judgement can crit. Atma's is extremely good and basically a must build. Zeal into Phantom dancer is likewise. The attack speed becomes important rather quickly for killing big creep/monsters, dropping towers, and any long duel/teamfight. Infinity Edge is good if you can sacrifice some defense, but it has a long build path where other items provide better incremental benefit.

Warmogs vs. Mallet: Its health regen vs. a slow. With a lifesteal item, mallet is probably the superior choice, but this could change if your team needs extra tankiness.

Damage Vs. Tankiness: I really really like clearing camps quickly. I typically outgold and outlevel every jungler I play against, this is extremely valuable. So I typically build movement and damage pretty much exclusively until lategame when teamfights start breaking out. Having massive offense is perfect for dueling counterjunglers and ganking, plus garen comes with a solid quite of natural defensive abilities.

Brutalizer/Black Cleaver: This item was freaking built for Garen. It was only after great consideration that I dropped it from the build. It should be worked into the build order if your team is ad heavy and the enemy is countering by building armor. Keep in mind the arpen stacks come when you inflict any physical damage, not just basic attacks, and this bonus applies to any attacker.

Tenacity: I've been tempted to build tenacity items a billion times. I say you get enough from your abilities and masteries now. Against very cc heavy opponents adding a tenacity item might be a good idea however.

Other defensive items: I really feel these are best when the other team is biased in one direction or another, ie. against a heavy ap team add some mr, or build armor against an ad team. The trap becomes that you build so much defense that the enemy can afford to ignore you in teamfights, this is bad, you need to make people take notice and flee.