What can I use to build my own spray booth?

You could pretty much build your own out of plywood and use plastic sheeting against the walls that you could periodically change. The more important issue is exhaust - you'll need an intrinsically safe exhaust system - alternately you'll need some sort of respirator so you don't get ill. Hope that helps, we built ours out of welded steel.

I was fortunate enough to have an old vacuum cleaner around. So it took it apart, fashioned some hose to lead from the box to the motor, then directed the exhaust out a window. The exhaust tube is situated in a hole I drilled into an old piece of scrap lumber I cut to fit into the window. At first I used a cardboard box, and that worked just fine. Later I came across some old plastic that I screwed together for something a little sturdier. It works ok. Its not as good as a biocabinet, but the filters in those can run major $$$. I also have a shop vac with a hepa filter on it that could easily be adapted to the same purpose without taking it apart. I hope that helps some. Other more experienced modellers may have better ideas.

I don't do much spraying, but when I do, I have an area on my work bench with a piece of newspaper on the bottom and cardboard taped together to make a back and two sides. It costs nothing and it works for me.

cardboard box, plywood, not a big deal .