plastic or glass sheet to repair shed (Amblecote DY8)

Hi lovely freeglers. The glazed roof of my hand-made shed blew off in the last bad storm and I'm looking for one or more pieces (depending on size) of either thick plastic (like polycarbonate, or the corrugated stuff) or glass to make a new roof with. If you're replacing glazed doors or greenhouse glazing or anything like that I'd really appreciate the glass. It needs to be at least 90cm long though, to reach across from front to back of shed. Many thanks in advance. Jane