These are 1/2 " PVC Fittings I designed to put together a Hoop House style Greenhouse. You could probably use furniture grade pvc fittings to build this, but I wanted screw holes designed into the parts. I did not put screw holes in the corner fittings as I didn't screw any of the 3 full length (hoop) pieces together, just all of the cut to length pieces were drilled and screwed.
The photo with the plants has these exact parts being used, but the one with just the pipes on the pallet has earlier designs. I needed to make some changes for strength reasons, as I broke some of the smaller/clip on style fittings. The pallet is just one I picked up for free a few years ago. You can make a frame with 2x4s and drill holes for the pvc to fit in. I put the pallet on a frame with caster wheels so I can move it around the yard as needed.
I bought 4' long snap clamps and cut them down into smaller pieces to clip on the insect netting and plastic. Good price here: http://www.greenhousemegastore.com/product/snap-clamps/pvc-fittings
Please check out my other things, I will be uploading more of the designs I have worked on over the last couple years.