I would start by finding out what the laws are concerning structures in your yard or attached to your house.
In my area, if the structure is free standing, there are no laws. But, if the structure is attached to your house, it must have a foundation 18 inches deep, and be able to withstand winds of 130 MPH.
My greenhouse is a lean-to on the south side of my house. It has an aluminum frame and super 5-wall polycarbinate glazing. It has withstood winds of 90 MPH. Mine is heated with thermo-solar panels but, if they are covered in snow or the sun doesn't shine, no hot water = chilly plants so I have a small electric emergency heater and a nature gas 'burner' that hooks into the thermal system. Our lowest temps are usually around 10 - 12F.
I do have friends who have built free-standing greenhouses and they last until we have a Zephyr, and then they are gone. So, even if you don't need a permt to build, I would try to follow the building laws for structures. And, common sense should tell you that a single pane of plastic or glass is not going to hold any heat.
Without some kind of supplimental heat or a heat sink, the inside of the greenhouse will be exactly the same as the outside. When I lived in CA, I had a twin wall polycarbinate greenhouse that I heated with 4 heat lamps. I set them 4 ft above the floor facing down to heat the plants below and the heat from the metal hoods radiated to heat the space above them. Our temperatures were in the mid-20's and I managed to barely keep the greenhouse in the 50's.
My daughter has a twin wall lean-to "temperate" greenhouse in zone 6a that she can maintain in the low 30's - high 20's (her lows are closer to zero) with a small radiant heater. She is growing citrus trees and azaleas and a few cold hardy orchids. I am growing tropical plants so try to keep my greenhouse above 50F.
So, as Bill asked, what are you planning to grow? Extending your vegetable growing season? Tropicals? Temperates?
