[simplechamp]

I've seen some homemade ones on the web. Mostly they look like a big air-hockey table, just a tray/box with a bunch of holes in the surface, and then a frame around the edge to hold the edge of your work material. Many use shop-vacs or the like to create a vacuum. Bigger the surface, bigger vacuum source needed. Of course it's not just the amount of vacuum pressure, it's the speed too. Pump A might be able to create more negative pressure than pump B, but if it can't do it fast enough it's no good.

The other part is what you use to heat up the polycarb sheets to get them soft. One guy doing small scale stuff used a radiant-type pizza cooker! But for your scale you'd need bigger. Some use really hot lights, or other types of radiant heat coils. Building a good heating system could be more work and more expensive than building the actual vacuum tray depending on how you go about it.

Being able to have the heater and former in one unit (heating setup over the vacuum tray) would be a big plus on the bigger scale stuff. You don't want to be trying to heat up the sheet at one "station" then moving it over to and clamping it down at another "station" if you can avoid it.