I built the one I use the most out of wood then lined the back wall with 16ga sheet metal. It works as well as the industrial units - I think the secret is in the gun, nozzle and the siphon arrangement. It's also important to keep the blasting media dry and pre-filter out the bigger blobs of snot - de-grease the parts before blasting. Paint remover is faster to get rid of unwanted finishes than blasting - depending on the type of paint, that is. The harder the paint, the better it comes off with the blaster.
Glass beads work good for aluminum, sand works best for rust. Paint remover works best on paint and it saves your media.
If you build one yourself, make sure you provide an air bleed to the bottom of the pick-up tube. Use safety glass for the window and keep the nozzle and the rebound as far away from the glass as you can. Waxing the inside of the glass with car wax a couple of times helps slow the pitting down, but not by a whole lot.
Scott
Consistency is a good thing....unless you're consistently an idiot.