That'll work.
If you like pie, and have a Safeway near you, you can use these instead for "free", for a more traditionally shaped UFO, if you buy the ones they make:
TMP link
I plan to use the black part on the top, and the clear part underneath, instead of the way it is shown in the link. Of course, you can use it the right way up too, and/or buy two of these and just put the two black halves together if you prefer.
I'm still looking for a suitable, shallow, clear plastic or resin domed saucer/shallow bowl for the top, which if I can locate, will serve as the command cockpit for the craft, complete with aliens lying on reclined acceleration couches.
It'd also look pretty neat with a clear, shallow dome over the black piece, if used the right way up, and you could then have a larger visible interior for the aliens to reside in.
May have to resort to vacc-forming for those options.
demonstrates how anyone can get in on sculpting for fun...
