I agree w/ the RoA on her, but the catalyst should be rushed. Doran's ring isn't going to help you as much as a ruby gem. I normally build her somewhat similar to anivia because she has good base damage and with survivability can be a true threat.

In that same manner I would go Merc Treads over Sorc, but that's also team comp based.

With ring gone, you open up a slot for Will of Ancients, which allows cassiopeia to solo baron. Extremely powerful yes.