runes: armor seals, magic pen marks, mr gliphs, ap quints
masteries: 9/21/0 getting cdr and magic pen in offense
build: start boots tome and one hp pot, finish a lucky pick, then get a giants belt. after giants belt finish t2 boots > black fire torch > rylais
at this point build vs enemy team:
other good items to get are: sunfire, bulwark, abyssal, morellos, banchee's, wooglets
example final builds look something like:
merc treads, black fire, rylais, morellos, sunfire, abyssal
Since you are amumu you are naturally pretty tanky and no one is going to be focusing you first so build more ap with hp thrown in so you arent just walking around doing nothing while you skills are on CD, your cry needs to do damage.