I am making a chocolate cake cheesecake with chocolate buttercream and wanted to know if I can put fondant on top of the chocolate buttercream?

Or should I just stop at the chocolate buttercream?

You can do whatever you'd like...just depends on the look you're going for. I'd stop with the buttercream...or instead how about chocolate ganache?

You can put fondant over it, but like ElizabethS said it all depends on the look you are going for.
What kind of design is it?