enhancement:
(Not really important, but it would make things easier)

If you could use the "Walls" option while using the "Sphere" or "Cylinder" etc. option in Area pieces would make some stuff easier.

I know you can get the same result if you "invert" your area with the same shape but only 1 smaler, but thats allways a bit annoying.

Hmm first I had my doubts ('is this going to complicate the already full Area configuration UI?'), but now I got some ideas to clean up this UI generally, and this would be a natural addition for that!