Lexan/Polycarbonate is the best choice for flat or non compound surfaces. As said above, plexi is dangerous.
When you start forming Lexan it gets to be a much bigger ballgame. GE has (had?) a really detailed information sheet for this task, probably online somewhere. I got mine in the mail if that tells you anything;-))
Lexan is hygroscopic, absorbs moisture, so it has to be slowly baked for 24 hours or so before you elevate to forming temp. Then, I can't remember the numbers anymore, but the forming temp is remarkably low and has a narrow window.
I'm not saying it can't be done, it's just a lot more precise than forming plexi.
My compound rear window on my Triumph GT6 racer was formed between two factory glass windows over the summer here in Las Vegas. The summer sun day after day formed that lexan to the shape of those two rear glasses, crazy what the desert can do...
Do you know the big bubbles in the MASH helicopters were the first big use of Lexan?