My SIL has two. One a quonset style metal hoop frame with greenhouse plastic for a cover. It lets in light but you can't see through. The other one is just an ordinary 2x4 lumber frame with more greenhouse plastic stretched over and nailed  to the West, South, East walls and also the South slope roof. North side is lumber. Thats where the flax bales are burned to keep it warm for the early starting spring garden plants.