I had a "Cover It" brand & used it for years without any serious issues. Mine developed some pin holes that leaked, but it still held up very well. Without exagerrating, I used it for 6 years until I finally built a real gagage & then gave it to a friend. He used it another 4 or 5 years until he finally got a house with a large garage. (He still has the Cover It too.) I've read some past experiences from others who complained theirs didn't last, but I think they may sell different grades which vary in durability.
I paid $550 in the early 1990's for a 12'x 20' with a double zipper door. It's important to prep the ground & put down heavy plastic under gravel if you can't put it on pavement. This stops ground moisture from evaporating to the ceiling & then dripping on your car (condensation). I also added a louvered vent at the front & rear walls which was suggested by the salesman I spoke with. Snow removal with a broom with a long handle is important or it could collapse. The most snow on mine was roughly 8" & it held fine. I always cleared it off in case we had more.
One thing I would suggest to avoid the pin hole leaks that can develop, would be to cover the frame with a plastic sheeting before covering it with the heavy tarp-like material they give you. Regular plastic will not last & disintergrate from the heat, but maybe there is a stronger one available, or even a UV protected tarp. My friend used the regular plastic & got about one year out of it before it broke apart in small pieces.
