My Sphere is a Vonjet sphere, this is a frame and panels. It also has a magnetic panel to access the internals, this way I don't need a wireless switch or screwdrivers to turn BB-8 on and off.
My BB-8 dome going to be 3d printed. My BB-8 head will use a magnetic connection to the body. The mount I am using is called the Halo Mount, it is designed by other BB-8 builders to be lightweight and require minimum force to move.
The electronics are fairly simple. The lights are Neopixels that are made into a strand. The sound is basic too just a mp3 trigger hooked up to a transducer that will make the whole body into a speaker.
I plan on using Joe's drive. It is a fairly budget friendly build that uses off the shelf electronics and drive frame is made of 3d printed components