Masteries
Defensive are my preferance, lets build damage items rather than defensive
Offensive masteries also work alright

Summoner spells
Ignite can be used in place of exhaust.

Runes
Pretty self explanatory,
HP quints can also be used
Magic resist glyphs can also be used


Alright so, item sequence

3 Pots + boots
Get brutalizer first, cooldown reduction, armor pen, damage, = awesome.
Get phage second, being able to slow opponents will be rather useful.
Get Ionian boots or boots of swiftness, I prefer the cooldown reduction but its up to personal preference.
Sunfire cape gives some nice hp and lets you do more damage when spinning / in teamfights.
Zeal lets you move faster, crit some, and attack faster.
I generally stop remembering to use pots around this point so I pick up vampiric.
Ghostblade is nice especially if you remember to use its active, which can be used for escaping, or immediately after spinning to get some nice damage off.
Mallet has a better slow = awesome.
Bloodthirster is a good lifesteal item for garen, cause 2 of his abilities are dependant on his attack damage.
Phantom dancer is just nice, super charged zeal.

You generally will not finish this build in 1 game, a game where you do well and it lasts a while you might get up to mallet, finish build in hour games only.