[habitat_gardener]

I agree about the venting and the party frame. I haven't had a greenhouse, but I have lost plants in cold frames that didn't get vented in time.

I visited a restoration nursery last year that had a lot of shade houses made with pvc pipe that looked easy and sturdy. Not sure if the photos will show up...they were an upside-down V shape, and the ribs were attached to the top with 4-way connectors. I'd use rebar as the foundation (slip the pvc over it at the base).