okay i have been using garen for a while and i know by seeing it your just thinking wow thats stupid but ive found its really worked well the runes are really up to personal preferene so i left it blank.

pros

you become almost unkillable
you become a great tank for the team
you can still dish out alot of damage to squishies
your ulti makes kills possible so dont think your missing out

cons

tanks are hard kills
you really dont become a great tank till you have thornmail
kills may not come as easy as you are hoping

starting off you should grab regrowth pendant and a health pot you should be able to lane well with your passive and regrowth giving you fast regen and a pot if you get dangerously low. next you want to get boots of swiftness garen can easily get early game kills and speed is the key to that once you have them then finish off warmogs. next you want to build thornmail dish some damage right back to them. next time is up to the team your facing if theres more then one ap char on there team buy force of nature it will help you greatly if not then skip it and go to sunfire. once you have a sunfire you can decide to become unkillable or add a bit of damage if im playing well i grab a infinity edge but if we really need the tank i build another warmogs.

ghost and exhaust is what you should be using to easily catch running away champs also as a escape method garens greatest strength in tough situations is his escapeablity with his w giving you speed and ghost you can escape very easily also catching enermy champs is simple.

what you want to do early game is hopefully get a couple kills for you and your ally i recommend waiting till level 3 before attempting a early kill so you can get decisive strike to catch them then use judgement really carves them up. as a tank later game if you are going for a gank always be the one to start the fight dont leave it to a squishie if things become to risky feel free to get out but remember 1 garen death is better then a entire team down. in ganks attempt to silence people nothing is more annoying then being ganked and nothing you can do about it when laning dont try to put yourself in danger its reckless in early games its very stupid. i dont reccomend this for people learning to use garen but i think he can tower dive like no other use w to protect against tower then hit e so they cant avoid it even if circling the turret.

yeah i just did this quick and wanted to put it out there because people really underestimate garen as a tank feel free to comment i know this build wont be used by many people but if you do use it enjoy!