I have this cloche that I bought a long time ago that I really like. It's light weight and folds flat for the off season. It's basically a few pieces of double-paned plastic
with some holes punched into the corners and a little vent cut into the lid. Fasteners came with it, but now I just use old bread ties to hold the pieces together.

I looked around for rigid plastic like this to make some more and couldn't find any till I took a short cut through the art department at McGuckin's and voila!
There were sheets of the plastic the size of poster board. Can't imagine what kind of art project would require the material.

I don't need another cloche anymore, but I thought I would pass the idea along. When it's time to replace the heavy rigid plastic on the permanent cold frame, I'll get some of this stuff.