This build is an amumu that does it all.

Runes
Magic Pen for maximum damage
Armor for jungling
MR for when fights do go down, as we dont get MR for a bit
AP per level will give you 20 AP and thats all we need.

Items.
Typical Dorans Sheild and Hp pots get the job done in the jungle.
Grab boots to gank a lane.
Farm Giants Belt.
Farm Sunfire cape, or Sorcerors shoes, again magic pen is great
Farm the other Sunire/sorc
Gank a bit as sunfire Sorc shoes is all u need for a little bit For another Giants Belt.
A ryalis gives you slows and Exactly 100 AP with our runes and masteries. Why is 100 ap important... that is when dispair gives you an extra 1% of their max life per second. Ouch! as well as 500 life.
Get a Force of Nature as it helps with the nukers and gives you move speed.
Pending on the team either grab banshees so you can ult NP or Just 2 more sunfires for maximum ouch status.

That concludes my guide to mumu, Enjoy!