use the stuff from smooth-on. Monster Clay can be used to fill the gaps. depending on what you want to do with it you can vary materials. I would love to see a WIP of it as you do it though.
Re: New "Rolling Droid" BB-8 From Star Wars Force Awakens
I had a concept for this that might give you full movement. Two nested spheres the center one weighted with rollerbearings and RC wheels. Holding the head with a strong magnet and a set of bearings
I have the same file. Im waiting to print the Chamber sides again as my last run on my Printrbot had some warp issues. I have some XTC-3D print coating that im going to use once I apoxie sculpt the cracks
PVC pipe, Pipe insulation, DAP contact cement, A yoga block for the head, Plastidip. Look the Plasti Dip artists group up on facebook and read through the FAQ. If you have questions we can probably answer them there