Can speak from personal experience having experienced several greenhouse collapses over the years. 3/4 pvc will definitely collapse in winter so will 2” and cattle panel style. The 2” pipe @ 20’ length can be made to survive if spaced at 3’ and you put in 2x4 posts at ridge under every hoop every winter all the way into may(had one collapse in April before). If you have any money for this project the best option for DIY is johnnys seed co gothic greenhouse benders, comes with instruction book. Mine is 14x68 and I never remove snow from top or sides. Sometimes the snow is 7’ tall up against it and it works perfect.