I most of the time start with a doran's schield because amumu is in the begin a bit weak
Then I take Mercury's Threads as boots for magic resist and reducing duration of slows and stuns
Is one off the things you realy need because its gives magic resist , Movement speed and it restores your health by 0.35% at each second
Sunfire Cape gives your health armor and deals 40 magic damage each second to nearby enemies