How much weight can 20 ft. 1/2" pex-b tubing support when using it as framing for hoop shed considering I intend to cover it with 2 layers of light- medium duty tarps and I want it to stand up to rain/wind and light snow in the the winter. The hoopshed with measure 20' long x 4.5' wide. I'll have 10 20' pieces of tubing along the length of the hoopshed very 2 feet with 3 perpendicular pieces connecting the hoops.
Virtually none. It isn't just about the strength, but the stiffness. It'll flop around like a fresh fish. Take it from someone who has done something similar with 3/4" PVC conduit and found even that lacking when a foot of snow landed on it.