I use a couple of 10 x 20 metal pole carports seasonally for my ultra tropical stuff since I am in a zone 9. The tops are the white poly that come with the carport. For the sides, I went to Home Depot and bought the painter's plastic on the large rolls.They are about 6 mil white plastic. I double it to make it 12 mil and then wrap the carport with it starting at the front of one side so I have as few gaps as possible. I attach it to the top of the carport/greenhouse and seal it with duct tape. The plastic lasts me about 4 years before having to replace it. The sun is pretty intense in FL so it might last longer in other places. I use a propane heater on really cold nights (under 32F) which we get at least 4-5 ++ times just depending on the year. I didn't run the heat at all this last winter whereas several years ago (2009) I had to run it for a month worth of nights lol.
