OK I bought about 400 feet of PVC pipe and some of those blue tarps (40x30, 20x30, some smaller ones too). I bought connectors of all shapes and sizes, including many 45 degree connectors, since I'm planning a special design. The goal is a reusable structure an inexpensive tarps that get replaced every year. Second goal is to have an inner, secondary cover over a few haches that I'll leave open all winter for ventilation.
If anyone wants to enjoy a large-scale tinker-toy project in the next few weeks, let me know.