Download the file package below. I have included a template of BB8's detailed artwork. I had help from my dad to put this up. I'm very bad at drawing. We used videos and images from the net as our reference.
Circular shapes can be achieved by using a compass. While straight lines which falls on the curved surface of the body can be traced with a tailor's tape measure.
The beveled edge can be achieved by building a makeshift styrofoam hot-wire cutter. I did that by recycling a piece of wood from an old picture frame, which I then used as the base of the stryo cutter. I mounted a metal stand-off at the middle as the pivot for the stryofoam. I mounted another metal stand-off for the hot-wire. The hot-wire can be stripped from a thick insulated wire. I then connected a switch and a 3.7v (18650) lithium-ion battery in series with the hot-wire. Whenever I press the push button switch, the wire heats up. Clean styro cuts for me!
You can reduce weight by hollowing-out the inner portion of the styro ball. You can do that by melting/ burning the styrofoam using a blowtorch or a lighter.