Montana 6,600 feet. 24x13 semi-pit. Attached to a garage wall. Very steep roof pitch (8-12). Use only from March (30 degrees low, 50 degrees high) thru October (temps the same). Summer temps (40 low, 85 high).
Considering single wall corrugated polycarbonate from Home Depot for the roof and single wall flat polycorbonate for the walls. Given that we are only trying to extend our summer growing season--not garden in the winter, is it worth the considerable extra expense for multi-wall? We plan considerable support for the roof panels.
One problem with the multi-wall: our roof panels will be about 16' feet long. We can't find a multi-wall sheet that long. So there would need to be a horizontal joint in the roof panels which seems to me a problem area. Corrugated single wall panels would require a simple overlap.