Best Material for Indoor Tortoise Enclosure Topper?

[LizzyLu]

I am building a large indoor enclosure for winter months, and will need to have a greenhouse topper. We plan to build a custom PVC pipe topper frame, but my big question is what is the best material to buy to make the actual cover? I plan to sew it to fit our PVC frame, but would like something thick, yet translucent to allow for viewing. Any suggestions? I know polythene sheet has been mentioned, but that seems opaque from the pictures I've seen. If you could suggest an actual thickness too, that would be great. I can deal with the visibility loss, if necessary. Thank you.

 

[LizzyLu]

We aren’t that far yet! Just getting the bottom frame & leg braces. Walls, etc still to come.

 

[Tom]

It would work better and look better to design and build a closed chamber with a solid roof on it and front opening doors.