Full AP Amumu?

I can say it is insane how he heals himself with just a in the jungle, and his damage is insane, yet he is squishy so your dives must be perfect, you could also benefit of tanky runes or AP-tank items.

Talking about it I've made an item for AP bruisers.

can you see my custom item? I've made an icon for it! http://boards.na.leagueoflegends.com/en/c/skin-champion-concepts/buOIBEzA-the-phoenixs-talon-icon-made-by-me-3

http://www.hiveworkshop.com/forums/pastebin_data/qd31zm/ThePhoenixTalon.jpg

It's not bad, had one in my last game. He lost it for his team when mf dodged his q and she 3 shot him.

But when he lands the q... Rip

You didn't want to finish your sorc boots right away which may or may not have been the right choice, but your reasoning was "they aren't building MR yet" which is backwards. Flat pen is best when their MR is low and becomes less effective as enemy MR goes up.