Last year I bought a 8x 12 easy-grow green house from Costco. I love it. It assembled easily. The weather stripping was the worst part. I used a screening tool and a putty knife to insert it. Quite tedious. The greenhouse itself is great and has tolerated high winds and storms without a problem. The vent opener is cheap but easily replaced. The benches are included. I wish it came in larger size. But for the price I feel it is a good buy. I would strongly recommend this as a starter greenhouse. I inserted a southern burner heater this fall. This heater is wonderful. I t takes up little space and is vented. The panels on the easy grow are UV protected.

Two years ago I bought an 8x12 Solex greenhouse which I am very happy with and found to be a good value for the money. I'm at 8000 feet elevation in Colorado - temperatures aren't especially hot but our high altitude sun is very strong and we have 300 days of sunshine annually. If I did anything differently it would be to put a door at either end and add more vents - I only bought 1 vent. We also cemented the ground anchors into the ground as we have high wind - which is somthing the manufacturer doesn't tell you to do - and this now holds up to our highest wind. You've also got to be pretty strong to snap the PVC connectors in this kit into place - my husband could hardly manage it. Whatever kit you buy, consider doing some underground insulation to keep your heating cost down.

Dorothy

The Harborfreight greenhouse frame is quite sturdy.
The instructions are poor but many posts on this site greatly simplify construction. Your concern about UV probably applies to any and all panels, so perhaps consider using the inexpensive HF frame with the intent to add protection to the panels or replace them with prefered plastic later.