Inherited a home built greenhouse once when I moved into a previous house. It was made with polycarbonate panels which had turned a milky yellow due to the UV rays in the sun. This also made them very brittle so the first strong winds of winter shattered the panes and polycarb shards went everywhere. Was picking the bits up years later. I'd go for glass if poss, or make sure the polycarb is UV stabilised so its less affected by the sun. As in other things you get what you pay for.