Tank Garen... what can I say but that this build has so much synergy. Maximizing Garen's passive by increasing his total health and then allotting masteries and runes that do the same will allow for Garen (at full build) to regenerate over 200 hp every five seconds. Recall??? I don't think so!

Ultimately, your goal in completing your mastery tree is to fill out Veteran Scars under the Defense tree and since you are playing tank anyway, filling in all possible defensive masteries such as armor, magic resist, and taking less damage are ideal. Finally, the defense tree should max out at 21 points. 8 of the next 9 should be placed in the utility tree uping Garen's health regen, experience, and this leaves one point left to place in either Greedor Cripple. It does not really matter which you place it in; I just find that having extra gold is more useful than an improved exhaust.

Now this is the fun part of the guide: the ITEMS! Now, being tank and trying to maximize Garen's passive, starting with a Warmog's Armor is a great choice to allow for as much time as necessary for it to reach all of its bonuses. To start the game, however, grab a Ruby Crystal as it is necessary for your Warmog's and allows yourself to be more aggressive in lane. However, before finishing your Warmog's Armor, be sure to complete Boots of Swiftness. I have searched and searched for the best boots for Garen and there is no comparison. The only possible substitute is maybe Ninja Tabi, but they do not have Enhanced Movement 3 and having extra speed is fantastic for chasing and running from being killed. If they ever come out with some Armor Pen boots, then switch to those, but that is unlikely. Now finish Warmog's Armor to maximize your health and regen capabilities. Now the order of your final four items will be completely different each and every game; it is completely dependent on your opponents. Ideally, Atma's Impaler and Sunfire Cape would be the next two; however, this combination leaves you susceptible to Ability Power characters since you have no magic resist. Against a heavy AP team, building Force of Nature as your third item is a must. The increased movement speed from this item is also nice alongside your Boots of Swiftness, allowing for even more speed. Atma's impaler is still the best way to still get your damage in while being a tank, so it is your bread and butter. Lastly, Spirit Visage is an excellent item to close out the build giving you even more health and increased health regen.

Against Heavy AD Teams

Against Heavy AP Teams

Against Balanced Teams

Early Game/Laning Phase
I am gonna start this off by saying, never jungle garen!!! Now that that is out of the way, you also cannot solo mid! So what does that leave you? Top or Bottom. Ideally, you want to say 2v2, generally done at bottom. Since you have a Ruby Crystal, at the beginning of the game you will probably have about 850hp or so. In this case, you sometime double the amount of health as champions you may face. As a result, using the bush to get close and Judgment to deal loads of damage can lead to early kills or retreating enemy champions. If they die, more gold for you. If they retreat, the goal is to block them off from experience and gold from killing minions. Meanwhile, your goal is to kill as many minions as possible to gain as much gold as possible.

Mid-Late Game/Gank-Team Fights
Since most Garen builds are done as DPS builds and since Garen is not a typical tank champion, being aggressive in team fights can be rewarding. If you jump into a group of enemy champions (followed by the support of your own team), many teams will focus you in the fight and not succeed. They will waste many spells and abilities trying to kill you and your teammates will clean up the rest. By the end of the fight, you will be either dead or low health and your team will be a lot better off than your opponents.