S4 Meta usually requires that a top lane champion is tanky for early objective seizure, along with tanky he should do quite a bit of damage. Garen Fits this perfectly, his ultimate has exrtremely high kill capacity in early and late game. Seeing that at scales missing HP he counters most of the top laners, even Renekton. He melts with his armor reduction on his Spin. Therefore with this guide you shall be able to deliver justice from the sky right to your enemys face with amazing effects!

Running flat Attack Damage Magic Resist and Armor allow for a smooth laning phase. I choose Flat MR runes because i feel that if they are going to have ap damage at level one you might want the flat ap than some small number like 4 bonus MR at level 1. Effective well against Teemo

Garen has extreme tenacity with his W so adding the Tenacious mastery makes him even more broken. Also 9/21/0 is just broken anyways. I chose the cooldown reduction for the obvious reason that he is not all about the attack speed.

Stacking on Armor and Magic Resist brings Health. And Garens Passive brings a ton of Health regen especially when combined with a Spirit Visage and a Warmogs if you feel it's applicable. You dont need damage when Garens ult completely blows up a champion in a team fight and also when his Spin stacks with Black Cleaver. A standard tanky build is perfect for Garen.

Maxing His Spin is the right way to go, however i choose to max the W over the Q because i play a more aggresive lane and when being ganked or in lane in general always knowing that you have that extra tenacity available from his W is great. If you time the Q after being slowed etc. then using the w youre escape is iminent.

Pros

His Ultimate completely dominates tanks, they make him more powerful
Ganking him is not easy, he has a cleanse and more tenacity
He can build tanky and still wreck and CS'ing is absolutely easy
He doesnt need life steal because of his passive

Cons

He falls off in extremely late game, but that doesnt happen often
As a tank he cant really carry the whole team
He can be bullied if you dont know how to lane well enpough

If You get stuck with any champion top lane that doesnt have a default tanky kit you might be screwed.
Teemo is the HARDEST thing to Play Against. I recommend maxing W. reduces the Shroom duration

Pantheon can be a trouble with his passive and equally magnificent penetration, he also doesnt typically build tanky which can be a tricky match up.

He absolutely destroys Some of the hardest top laners to fight against.

Nasus is so easy to deny stacks early game with his Q, also his ultimate only makes yours stronger.

Renketon is the same if you silence his as he dashes onto you and then use your W you can cut the stun time by a lot.

Yasuo is an extrememly easy match up for Garen in top lane, your spin proks his shield and then you can continue to damage, denying his dash with your silence.