Hey guys this is my first guide so it my be a little sketchy... just warning you. My main idea of this build for Amumu is to regenerate lots of health and mana so he can use his abilities(like despair) more often and longer with mana regen and stay in battle longer with health regen.

I picked Flash mainly so Amumu can flash into and out of battle in dire needs. I usually have Exhaust to slow enemy targets so my team can get the kill(unlike using ghost to just your advantage). Or i get Teleport so I can get into a team fight quiker.

I went with armor and dodge chance first with Ninja Tabi, then I went to build on health, health regen, ability power, and a little bit of AD. If you like a more AD Amumu then I suggest getting Hextech Gunblade instead of Will of Ancients. But the main idea of these items builds is to have lots of health and armor so you can stay in team fights for a long time.

PROS:

Lots of health and health regen
Can stay in battle for a long time
Can jungle........ Sorta

CONS:

Squishy early game
Not so great damage output

Thanks to all who viewed this so it can acually be call a guide and be used as guide. It would also be great if you could rate this(if you have time to) and if you have any questions or concers or think there's a better way to build Amumu please leave a reply for me. I hoped this build helps!