Hi, its my first build. :)
So here I bring you build for carry Garen. It means, that YOU will be guy who fight the most of his team and your team rely on you (well + youyour tank).

For runes I like to go dogde seals, armor pen marks and cd reduction glyphs.
-Dogde seals : Just works great. My favorite.
-Armor pen marks : Can help you at beggining.
-Cooldown reduction : Good ones too. The most important thing about it, is that your cd on ulti refreshes faster. To let you know, most of your kills will be ulti kills.
-Flat health quints : just HP.

Ok now lets go to items.
- Begin with regular boots and 3 hp potions. This will help you get first blood, if you have good lane partner.
- After boots go buy Sunfire Cape. Works really great. You can farm minions faster and start to fight agressivley in team fights.
- Finish boots to level 3 boots.
- Buy avarice blade - Gold will come to you faster and you get extra critical strike.
- Now its time for Guardian Angel and Force of Nature. If you dont have problem with caster start with Guardian Angel, otherwise start with FoN.
- Infinity Edge - Crit chance for your jugment and dmg to crush your enemies.
- FInish Youmuus. Use combination [ Q + Youmuus + Ghost ] alot.

For spells I go with :
- Ghost - great for chasing and escaping.
- Exhaust - Just nice to have it.

Other spells I recommend:
- Flash - can change ghost with it. Good for lane movement, but lacking late game.
- Ignite - Can lend you few kills early game, but you will not use it later, because your ulti will be better finisher.

Other Informations :
- Do not fear to get info heart of fight.
- Use your Q + E combo when you get snared.
- Use your passive alot. Its really one of the greatest in LoL.
- After getting full build buy 3 stat potions.
- ALWAYS use your ultimate as finisher, NEVER as opener.

So this is the end. If you have any questions just write the comment.
Have fun and enjoy Garen, The Might of Demacia !!!