First yr we used 4mil poly from TSC and it made it through the first Winter. Last Summer we PU a real 6mil GH sheet that was a left over at a large commercial GH. 25 x 50' for 25.00. Quite a deal. That's enough for 2 coverings of the top and front and should last 5-7 yrs each.
Hi Ken. Let me know if I can help. My design has worked out very well for us so far. 2 yrs this Jan since we broke ground for the GH. We are in trout country but you can suit the design to your area. It is by far and away the most fun farming we have done and for us the GH is such a treat on these cold sunny days. It was high in the 30's today and the GH hit around 85F.