not at all, there’s a couple things that go into it:

the body is just a glorified beachball with a segway inside of it, you can tell from the way it bounces forward and corrects it’s orientation. the top would be bit more trouble, but not by much, just a circular lid with a few ball wheels and a sensor to see where the lid is in relation to the top of the internal segway. program it to always be on top of the seqway or however you see fit, and there you go, your own bb8.

brb, going to make my own.