I go full tank with Garen because his ratios suck. Only two skills scale, and that is his Q and E. The scaling on Q is pretty good, but on E its a joke. For this reason I build Garen full tank. His base damage is still pretty high, and ult has great assassination potential.

Items: Merc Treads, Sunfire, FoN, and then based on the situation/other team comp I will go Thornmail, Banshee's Veil (yeah, the mana but the shield makes up for that) and then GA. And for summoners I get exhaust and ignite. Early game, I just go for kills until I get Sunfire, then I split push and farm like mad to get other items while helping out in team battles. Late game I soak and take out the enemy tank or their dps, situationally. At least thats how I play Garen. I just don't see the investment with damage items when only one ability scales decently. Of course you could always get an atmas in place of the bv or ga, but I prefer the extra armor and mr.

Anyway, thats my two cents. And I'm unorthodox when I play Garen as I max Q first. I prefer the guaranteed damage on hit and use sunfire to farm mid game anyway. I still get double digit kills (high deaths though), and crazy assists. And, in fact, I do way better late game than I do early game with Garen. The exhaust and ignite combo help immensely. Anyway, again, that's how I play Garen

I go straight tank usually make the enemy damage themselves thorn, sunfire, and spin to win

Atmas Warmogs, frozen mallet really helps his damage. Late game he's really only utility and his ulti for the effect of FINISH HIM. FATALITY.

I play Garen a lot and unless they buff him in some respect, your never going to be a powerhouse in the late game like you are at the start and mid.

What I do with Garen my building order is Dorans Blade, boots(Ninja Tabi or Mercs depending on the other team), Brutilzer and then depending on how your doing you can finish up your ghost blade, or get a giants belt and start building your defenses up...

Giants belt turns into ether Warmogs or a sunfire cape, if the team is heavy on AD then get a sunfire, AP then you go warmogs. And if/when the game gets into its late phase and your attacks aren't doing much, this is where you can make the difference between being useless, and being a huge asset, and you figure out what you can do by asking yourself these questions.

1. Does their team have a tank, or a very defense heavy player?
2. Who is the most venerable to being silenced?
3. Can I run into their team, and live long enough or escape so my team can attack without fear of being killed?
4. If I find myself unable to do any of the other things, am I better off building support items?

Garen has one of the best ults in the game, for the sole reason that its like playing with all your enemy's having 20-25% less health, once you get them that low its a done deal, what also makes it so great is that it does base magic damage plus extra for all the health they are missing, which means in a late game fighting an Alistar who has 3.5k health, even using your ult when he is at 50% will do a crippling amount of damage which will allow your team to kill him that much faster and get him off the field, and the same goes for any tanking champion or bruiser.

When used correctly, your silence can mean the difference between the enemy's Annie getting off all her spells and Tibbers to destroy your team, and your whole team killing her in the blink of an eye with all their spells at once. Yes its that important and the great thing is, if you use ghost blade with Decisive Strike will allow you to catch even a fleeing Yi.

Garen is not a tank but until his damage is buffed for late game fights, your only role in most team fights comes down to you running in and doing your best to stay alive while your team comes in and starts taking them out while their spells are focused on you, hence why you want a couple tanking items in your build even if your a full AD Garen.

Sometimes even with your best setup and a good team, the other team might just be to smart in not letting you ult their tank, silence their carry's, or they ignore you and kill your carrys instead of wasting attacks on you, those games happen. The best thing you can do at that point is play a more supporting role by getting Starks Fervor, and a Legions, both of which make a huge huge difference to your team. You might give your AD carry that little bit of extra lifesteal he needed to kill that Morde that was stomping your team before. At this point all you can do is stay alive, and do damage where you can, every little bit helps. Also get an Oracles elixir and do a bit of ward killing, every little thing only helps your team.

if only Judgment aplied on hit effects ..

Here's what you can do: play Warwick. Lament at his late game. Go back to Garen. Rejoice.

1:sunfire (you can live without it but it seriously improves early game farm, and early game damage output is pretty equivalent to a dps item)
2: atmas
3: warmogs (frozen mallet optional as well)
4: phantom dancer
5: infinity edge

The only time i lose as garen with a good score is in solo/duo queue games because the dps can't seem to do their jobs right, focusing raid boss singed is good right!?

Most of my kills come from the lane phase or ganks on mid, so not really steals. I often find myself sprinting through the enemy lines late game to that carry with almost no armour items, and well, q>e>r, and bam one of their main killers is dead. Garen can be an amazing anti-carry late game if you can get in there for a silence. The ult is hilarious, I can't remember how many times i've been chased on 1hp by someone at 20%, and just turned around and slapped them with Demacian Justice. Favourite champion by far.