This build is a build which helps Garen become a carry while being impossible to kill. Starting off with a very easy to farm build which leads to more minion kills (gold) will help you finish your build quickly giving you an edge when late game comes around.

Amazing skirmisher (1v1)
Great in team fights
Durable Fighter
Easy to get kills with him
Great at ganking

He CAN die
Spin has a cooldown

The runes I chose were armor pen and cooldown reduction. Since Garen is only restricted by cooldowns I get as much as I see fit through runes and finish the rest off with the new boots of pwnage. This gives around 30-35% and will help you a lot when you are waiting for your finisher to come off cooldown or just need that extra spin to win!

The masteries I chose focus on his offense since you will be working on his defense early game (offense scaling is a also better through masteries) I did not get the attack speed over the damage because you won't be auto attacking "too much" when it comes time to do battle. The extra damage you get is added to your spin damage, and so are the % of offense abilities. Getting armor pen helps garen as well as the critical strike. Utility is not bad however using this build you will have plenty of cooldown reduction, and although I love being a speed fanatic, the 3% movement is not worth giving up 5% damage.

Exhaust and Ghost are my preferred summoner spells because you will NOT get away from Garen, it also helps get away from any fight as well if you need to. By using ghost then spinning to remove slows you will be at unrivaled speeds when you decide to pop Q. Even rammus will get mad and stop chasing with your force of nature and phantom dancer. However I can see where ignite is a good option as well but I would never replace Exhaust especially after they changed it. It is far too valuable for shutting down a carry or helping pad the damage of a team killing ultimate.

Having boots first is a must have because you can harass and escape a lot faster than anyone early game using your Q. It will also allow you to make sure all your spin hits land on your desired target. Next I would grab a sunfire cape not only because it's the perfect item for a Garen, but the reasoning behind it is that this drastically increases your farming capabilities. In team fights you can grab assists by being next to them (if your spin is off cooldown) thanks to the sunfire ticks, and in lanes you can knock out entire creep waves by spinning alongside your firecloak. Force of nature is a good item for the movement speed+magic resist seeing how you already have armor. HOWEVER, if the team is heavy physical damage I would NOT get a Force of Nature Instead I would get a thornmail or Randuins Omen, depends on how you play (if you are fine with activating your item Randuin's omen is amazing due to the effect and also health regeneration.) If the team is balanced my build works fine, and if they are heavy on caster dps, I would still get a sunfire cloak and all the items I recommend, however you could switch your boots to the Mercury's treads to pad the damage a little better. The point is using your W you should be able to eat any nuke damage and then go in for the kill, caster's are squishy and if you face a vlad your damage output will still be high enough to dominate him with your sunfire cloak and spin.

As the laning phase starts try to pick a lane with a anyone that has any snare or slow if you can, this will lead to getting a full spin off and overwhelming your opponents in the early game. Also do not be afraid to take damage as long as you dish it out, your passive will help you regenerate faster than opponents so take advantage of it. I normally grab one health potion but you can decide how many you want.
The fun starts when you farm enough gold for your sunfire cloak, this gives you extra damage all the time and spinning on a minion wave will lead to very fast gold farming. You will also have your cooldown boots by now so do not hesitate to execute anyone thats low on health. In team fights you should look who is on your team before you charge in. If you have an actual tank (Galio, Shen, Rammus) or someone with a large disable (Ammumu) or even a poppy, let them engage first and follow them in and focus on doing damage to their easiest to kill character. If you have to lead the front, be ready to take some damage and make sure you let your team know who to kill first.

Overall this build has been very successful for me, even in ranked games and I hope you enjoy it. Comment if you have any questions or want more information :)