I mentioned that I went to Home Depot and spent a bunch of money and didn't get anything useful. Specifically, while still trying to get a 4' x 8' x 1/2" PVC sheet, I picked up a 4' x 8' x very thin PVC sheet. I was thinking this would be workable, but not really ideal. It was also expensive.
$57.67 for the sheet.
It seemed flexible enough, but just didn't provide any benefits that I could tell compared to the vinyl flooring. My understanding is that they're very similar materials, the vinyl flooring is just a little bit thinner and has a print on top. You can probably see in the picture, but one side of the sheet was textured - I think this is undesirable because it either makes it more difficult to adhere to the plywood, or it causes unevenness when attaching the other hardware.
After looking through the Home Depot selection of angle metal I found nothing that was exactly the piece listed on the BOM. There were a selection of 4' pieces, but nothing particularly usable. I ended up getting 1 1/2" inch punched steel, but it's not uniformly punched. I'm not sure who had it in their diary, but someone warned against this as it makes things more problematic. Either way, as I noted before, it was more expensive than anticipated and not ideal.
5 x $24.80 per 8 foot section = $124.00
I visited a local metal shop - Loucon Metal Ltd - and they have an awesome selection. They don't have anything punched at all, and it would be $84/hour to have anything done. It was very neat visiting the shop - all the different widths and thicknesses and geometries of a whole bunch of different materials. I talked to the guy there about what I was trying to do with it, and as with everyone I talk to I'm sure he's positive I'm going to grow pot. Regardless, he was very helpful, and lead me towards architectural aluminum. It's lightweight, it's attractive, it's easy to work, and it's more suitable for the humid environment than steel. Structural aluminum would be quite a bit more expensive, and for the spans the food computer is dealing with the architectural will hopefully do. I confused myself while ordering, and ended up getting an extra 10', so that wasn't ideal, but at least I have some room for error now. I had them do up a quote for the same product but in steel, and it was about 2/3 the price - for the ease of working, I figured it was worth the extra 30$
5 x $17.44 per 10' 6063 T5 aluminum angle, 1-1/4" x 1-1/4" x 1/8" = $87.20 (should have been 69.76 if I had ordered the correct number).
1 x $11.31 per 7' 6061 T6511 aluminum flat bar 1-1/2" x 1/8" = $11.31
I'm hoping the aluminum and the vinyl will serve me better than the steel and PVC.