Garen: Spin to Win

Genetically superior to normal people due to the fact he cannot seem to get motion sickness. Garen leads the way in spinning-based attacks. But the key to Garen isn't killing, it's not being killed. The Way of the Tank as some say.

Master of The Spin

Garen
The Might of Demacia

The build that I've gotten most success out of in the meager amount of time that I've played as Garen is a completely tanky dps build. First, you build Ninja Tabi, as I find that it's very effective against characters that deal massive amounts of auto-attack damage, as it cuts their attack by a tenth of its normal power, and that isn't even compensating for your armor. Then I go for the Sunfire Cape, the armor and health it gives is imperative to any tanky Garen build, plus the added DPS is nothing to frown at. The next thing I go for is a Warmogs for the huge amount of HP and HP Regen it gives you. My philosophy is that Mage's can't do very much against HP Tanks, so there isn't too much focus on MR other than your damage reduction skill's passive. As a health tank, you only need MR late game, when the mages on the enemy team have AP up the wazoo. Then, on the other half of the build, I focus on AD, I first get a Brutalizer, because you have to make what little damage you have at the moment count, and it gives a much needed cooldown bonus that can shed seconds off your cooldowns. Then, if you still haven't won yet, you should be in late game, this means you'll have to prepare yourself for more powerful AD characters, If you are facing a few AD carries, then I suggest getting a Thornmail, as it benefits you greatly on both damage and survivability. The next choice is situational, I actually haven't gotten this far in a build but I will give some options, Guardian Angel, if you're failing hard, or maybe an Infinity Edge if you need more damage for pushing turrets, or possibly a Force of Nature if the enemy is starting to use Magic Damage heavily.

Perseverance

One of the best passives in the game, this heals Garen fully in approximately 200 seconds, coupled with HP Regen items, Garen can run off for a moment and come back with a major portion of his health back. You shouldn't let Garen have this buff on him or you'll be severely outmatched after a fight and you think you're both low on HP.

Decisive Strike

I love using this on mages, mainly because of the silence that makes them virtually useless. This is also good to use when  there are five or so champions trying to kill you and you just kick into overdrive and sprint away. The damage portion of this spell is useful as it adds your damage to a set amount depending on the level of the skill.

Courage

Very useful for getting MR since something you naturally should do, which is killing minions, increases your Armor and MR. The active on this is very good for teamfights since it limits damage done to you by a ton and your enemies will rage as try uselessly to kill you.
Plus you shout "DEMACIAAAAA", nothing ever goes wrong when you shout that.

Judgment

You basically do damage to the area around you by spinning... Spinning to win. Judgment also removes slows on you so you can escape your enemies much quicker. It doesn't really do much damage until you get it to high levels, so don't plan on this being a game-changer unless you go AD Garen, which I suggest you don't do.

Demacian Justice

There's not much that I can say about this skill other than use it as a finisher. It scales on health lost so use it when they are down. Probably not the greatest ultimate late game as people can be finished quickly, but when you have low level fights this can be the great decider.