Thanks resdog! Well, they do lay quite flat, I was thinking 1/4" also but the tell me lexan is pretty strong stuff. mine is screwed through oversized holes with washers for expansion and theres a SS lip on the top edge that makes water shed over the top. May I ask where you got your lexan?
I used tinted acrylic. For my use there was no reason to go with Lexan (polycarbonate). We use a supplier called Cope Plastics. They have offices all over the US.