What runes should I use for Amumu?

I currently use armor pen, health at 18, and cd reduction for red yellow blue respectively.

My item build is.
Chalice
Mercury Treads
Sunfire Cape
Sunfire Cape
Abyssal Scepter
Doesn't usually get this far.

With that build which runes would help me the most. I like to be able to both tank their entire team for around 6 secs, while still being able to do good damage. With items/passive i have 60 magic pen, so idk if i really need the magic pen runes or not, but i dont know what other ones i should use for marks. Also wondering what other Amumu's use for seal and glyphs.

Bump

I get all AP. I'm weird like that.

I tend to focus on Merc treads, sunfire cape, and what is it frozen heart? Something like that if im feeling like a jerk ill just get thorn mail as well.

But rather than focus on output I focus on armor so that I can take hits and let my passives do their work. And there are a few armor that give ability power as well which is just sexy because then R becomes a monster ult.

I'm rethinking getting magic penetration runes. Since magic penetration is applied after magic resistance reduction it seems like the pen might be useless. I generally get an abysaal scepter, which reduces magic resistance by 30, and Amumu's passive reduces is by 40. This means that magic penetration will only help on targets with more then 70 magic resistance, which will most likely only be 1 enemy per game. I don't know what else to use for marks in the place of magic penetration though,

Personally, I don't use Magic Pen./armor pen. at all, nor do i use cd reduction either. I have about 35% health regen. per 5 seconds 35% health regen at lvl 18 and 30% either crit chance or just +X health per lvl. and my quint. is +health per lvl. But I use Amumu as my main and i use him as a tank/assist, initiating team fights with bandage,despair, and tantrum into ULT. works well for me but might not work for others. Also my items are Phil. Stone, Ninja Tabi, Leviathan, Warmog, Abyssal/his last recomm. item (forget the name) and if there is time, Guardian Armor. I seem to not die often, and really help in team fights....granted...my assists heavily outweigh my kills. but such is the life of an assisting tank :P