Believe me, I wanted to use Aluminum as I have about 3 square feet of it, but to do it safely, it would have meant a reasonable tool investment which negated the cost of just ordering pre-made ones from someone else. There's also the time involved. My 2-layer acrylic boards are pretty stiff and fit the camera tightly. I had the acrylic, the adhesive and the appropriate hole saws on hand.
I've run into the same sort of issue in wanting to make myself a "fancy" dark cloth. At a local fabric store, the only outdoor water resistant and breathable stuff they had would have cost me $50 alone. then there's thread, velcro and/or elastic cord. plus, we get into the fact I haven't run a sewing machine in something like 20 years. A dark cloth becomes a weekend project. Nope. Materials cost+time kick it right into not making any sense.