Garen is probably the best solo top ad carry in the game at the moment. He provides huge burst damage and allows for huge plays to be made. he has no true counters and outlanes almost anyone

Pros:
o High burst
o Incredible sustain
o Good Custom skins
o Good range on abilities(the spin)
o and has a shield to tank even though u dont build any tank items

Cons:
o Bad at pushin
o Has trouble killing turrets
o Outlaned by solo top nunu
o High skill cap champion
o Patience
o Always banned at most elos

I take flat hp marks because garen shines late game and has some trouble in early game. I also take flat hp seals to survive the other solo top champions incredible burst damage . I then take flat ad glyphs so I can dish out the much needed damage.I then take Alacrity quints so i can auto attack more and this works incredibly well with the flat ad glyphs.

arens a dps so naturally you want to take the masteries that will do more damage but
you also need some survivability even though your shield usually is enough to defeat all.

I go brawlers to give me that early game burst that garen owns with and i take two hp pots incase my passive isnt enough I then buy a avarice blade to start getting more money because garen is nothing without a ton of items. You then buy a pickax for more upfront damage and leave it to sell later. At this point you need some lifeteal and more hp the dorans does just that. I then get a sword of the occult because garens a champ that snowballs hard and is unstoppable lategame. At this point your lacking some movement speed so we buy basic boots. Next we sell the dorans sword and start building bloothirster because garens auto attacks are his main weapon. You get another one to just dominate in mid game(make sure you have both by mid game). Buy another dorans blade for survivability then buy lvl 2 boots and sell dorans blade for your madreds blood razor.