You maybe know it but more Rammus has Armor, more he do damages. Next, the mastery, exhaust and mastery for AP, i've got this for Cooldown Reduction (Sorcery).So the ultimate do more damage and the Powerball get more Cooldown Reduction, to escape and get all the champions who flee often. I've choose exhaust in the mastery because i don't think everyone use just Rammus, so for those who use Exhaust, it's a bit cool. If you don't care about champions fleeing, or if your ennemy don't focus you, don't take Ghost OR Heal and take Ignite.

For the runes, I took so much armor runes to get more damage, it's the point of "Apocalypse Rammus"; but you can always change for magic resist.

Ps : Look at the build description, I tell why I use Mejai's Soulstealer.

Another Ps : Don't vote without leaving comments !

Hi there
I notice that you've got "mejai's soulstealer", as I can see you're a tank and therefore i find it a little confusing that you have ap stuff. Your masteries also increase ap, no need of that. And you've exhaust in masteries which is very weird when you don't even have the spell :)
Anyway pretty fine Rammus build. I would recommend not to have armor as runes becouse armor is so easely to get.

Don't hesitate to post comment to help me to make this build more constructive !