great!!!

i replaced my frozen mallet with warmogs, for the increased health regen and survivability.

hmm, frozen malet is no need if you got Randuin's Omen
i would take one more phantom dancer insteed of frozen malet :)

It's quite a good build, but I have to say this: When you play Garen as a Tank/Dps this build apparently is a mix between those, you should always get Warmog's since it now gives +920 Health and the massive hp regen. Indeed, if you're going for critical Garen you want to have critical runes, but if you dont got enough IP to buy runes I advise you to change them to armor penetration runes, since more champions use those. And on the skill build, Decesive Strike is better to max before Courage, since it gives a very long silence, good damage and you can finish off champions much easier. Furthermore, a good build +1