I have a tempered shower door that I got for making a cold frame in the garden. I got to looking at it and was wondering how it would work out as the front pane on a plywood tank. Its at least 1/4 maybe 3/8 thick, and 3 X 5'. How big a tank could I build? At this point it is only a daydream, but since it appears that several individuals have made such tank here, I figured someone would be able to tell me.