I was stumped on this one for some time-- I needed hoods too, but juggling large, slippery sheets of glass 8 ft up in the air was out of the question.
Problem is that-- ANY flat plastic sheet (whether acrylic, Lexan...) will bend and sag (especially under lamps). Thicker sheets do warp slower, but I'd think they also transmit less light.
So- I figure the best solution is thinner acrylic sheets (1/8"- 1/4") with a supporting frame. Here's my suggestions--
1. Measure dimensions for hoods & have local acrylic supplier cut up 4x8 sheet-- NOTE: acrylic cut dimensions should be 1/8"- 3/16" less on each side due to framing thickness.
2. Scratches from cleaning could eventually block light transmission, so specify "acrylic", not Lexan... Everyone (even some in the industry) will tell you that Lexan is better & stronger-- And yes, while Lexan is more "impact resistant" & expensive, it is less scratch resistant than acrylic.
3. Price out the 4x8 acrylic-- it can REALLY vary.
4. Buy Aluminum C- channels from Lowes or HD (in hardware) with depth corresponding to acrylic sheet thickness (1/8" or 1/4"). Aluminum won't rust, & its easy to cut.
5. Trim out 45 triangle on sides of C-channel at each corner of hood. The Aluminum may break when bending around corner, doesn't matter. To adhere channel to sheet, use Silicon, 3m acrylic adhesive, or some foam tape?
6. Hope it works- mine havn't warped a bit, & I just wipe w a microfiber cloth to clean.