The next part was very tricky – I had to cut the round “skirt” out of styrofoam.
I simply cut the circle of the size of the head hemisphere.
Then I had to cut it at an angle – I checked in the 3d project (I used Sketchup and downloaded two BB-8 models from the Google repository) how wide should be the top and bottom of the skirt.
Then, using compass, I draw the smaller circle on the other side and started precision cutting with brand new, sharp paper knife. It took a lot of precision and time to make it but the final effect is very nice (of course – it is upside-down in the picture):
Then I cut holes for the roller balls:
BUT! I did not like it as the attachment was not precise and I did not have any good idea to keep these in place. Fortunately enough, I was inspired by another BB-8 Builders Club member to make a separate platform with roller which I figured to make from this old tray:
I cut small holes using driller and glued the rollers into place. I had a lot of luck at this point as these fit, roll nice and the distance to ball is perfect! No need to change it
Here you can see how nicely it fits, there is just a little space between the skirt and the body (again upside-down):
Eventually, when combined, body and head begins to remind the real shape of the BB-8:
Still, I will need to cut one more ring to put between the skirt and the hemisphere as in the movie it has that silver ring in that place.
This, however, should not be that difficult anymore.