i actually made it out of paper mache and cardboard...
-i cut out 6 sides out of cardboard, and taped five of them together. (cuz its a lot easier to mache the inside if the bottom or top isnt on)
-cut out a cat sized circle entrance
-i paper mached some layers onto the outside and inside...at least till its strength was to my liking...he can lay on the top and it holds up fine
-then i taped on the bottom (or top)
-this was the hard part, paper macheing the bottom onto the sides by sticking your arms thru the entrance hole...you cant see a thing
-the last layers of paper mache were paper towel, to smooth out the surface...i left the inside news-papery...im sure the kittay wont mind
-before that layer dried i used some watercolors on the wet towels to make the whole thing greenish blue
-i didnt like how it looked so i masked off certain spots to look like trees and just spraypainted the whole thing...and tah dah!
yes it is a parallelogram! you know why? cuz my cats name is Rhombus! i just knew i had to make him a bed of his namesake
he likes nomming on lots of things...but its only random things...he loves straws and cardboard...but he's sat in it while it was still under construction, and the only thing he nommed on was the tape i used to mask off the tree design!
and if i end up putting it in a different room...i may use your moon idea