Ok first and for most.This is my first build i've done for this site so any good suggestions will be taken sersly.Now down to bis with this build.
This build is meant for a supporter / Gank support role, however when you look at it he could tank as well but we gonna say you got a ganker on your team and you will be a great support for those ganks.Also you will be very useful in team fights and team pushes. Learn how to use him right and you will get fed or help feed your ganker. Now YOU WILL NOT WIN every game or every team fight...hell you will not get every gank but the right team helps out a lot (I like to have two ranged class with me one physical attack and the other a mage class) but you cant always have what you want lol so lets getting down to the break down of the build shall we?

For Marks i like Greater Mark of Desolation x9
This for the simple fact physical attacker hmmm armor pen hmm need more?
For Seals I like Greater Seal of Health x9
think about it you are a supporter/ gank support role makes some sense now? first blood mean anything to you?Well you stack these and you will have +48.15 to health from these to start with thats rather big when you think about it
For Glyphs I like Greater Glyph of Scaling Ability Power x9
Yet again think of your role need more info as to why just quit now cause you wont get it
And for Quintessences I like Greater Quintessence of Health x3
Now I go with these cause of the early game out put from them more life the harder it will be to get ganked and easier for you to get fed but if you feel like there is a better one out there for you go with it

Ok so you look at them and you go make some sense but you also wonder a few things
1. burning embers-well early game my friend and a little late who would not like +10 ability power?For just having something on CD
2. points in Utility-well all for the support role and greed helps to get your items just a little quicker remember your role

Now as for the items they are all great support when you think about it increase attack speed just helps in team fights and ganks.The life leach to help keep your *** alive
But when it comes to the order it can change to what you need in the game. as well you may not need some items like for instance Banshee's Veil so go with what you may need. If you got a lot of physical maybe Thornmail or Sunfire Aegis to help with that little more dps to take them out. Now remember change the order to your liking and change the no need item for this game to what you think is best for that game

For this build go with Ignite and Heal
Ignite for two reasons masteries buff and use it at the right time early and mid game you can kill that almost dead champ running like a bish
Heal well duh your role support support gank support you can save your self or an ally so yeah its nice aint it?
Now if you want to change a spell i would go with Teleport or Exhaust
Two very good spells for supporting

Well there you have it hope you like this guide but there are a few more things to cover.
If you fell like you can get fed with this build then ask to solo a lane. Garen can become beast if fed early game and this build will carry the team for mid.If you just want to really be the support role and dont care to become beast mid game get a ranged with you in your lane so you can have them harass the other team and hell you two might get a kill =D