I used a similar structure (roof only, no walls) and it lasted about 5 or 6 years in Wisconsin. The key is to get it anchored securely. I also found that it was helpful to replace the bungee cords that hold the edges as they start to stretch (it won't shed son well and the top flutters if it's not taut). Also I ran 1/4" rope in tight diagonals in each rectangular roof space. It stiffens the structure a lot, and provides additional support to keep it from sagging as much with now load. After each snow, I'd go underneath it with a push broom and bounce the roof to make the snow slide off.