I followed the instructions for building a simple spray booth I found in this article in Fine Woodworking magazine. (Link to the article can be found here.) The two illustrations to the left sum up the most relevant info nicely. In summary, the booth is made out of rigid foam insulation and the sides and back are fastened together with duct tape, so it is lightweight, foldable, and easy to transport. The back panel has a hole cut in the center into which a furnace filter is placed. A box fan is set behind the hole for drawing air through the filter.
The booth is placed in a way to take the best advantage of the room's air circulation, with sources of fresh air in front of it and a means of venting painty air behind it. Since there is no actual ductwork to contain the fumes, the booth does not exhaust them completely, but I can attest that it does cut down considerably the painty mist that otherwise hangs over my work area.
It's important to note that this booth is only for water based paints such as acrylics. It is definitely not suitable for solvent based paints, that's a whole nuther animal entirely!
Right, my own booth in progress. I used one 4' x 8' sheet of 1/2" thick insulation that I purchased at the local lumberyard. I chose a white color so that as much light as possible would be reflected back onto my work. Since the fiberglass inside the panel was very irritating to my hands, I also put duct tape over all the cut edges to contain it. It's white, so it's hard to see here.
Left, making sure the furnace filter is installed correctly! The arrow has to match the direction of the airflow when the filter is installed.
The filter is a basic, inexpensive one. According to the Fine Woodworking article, a higher grade of filter, one that could screen out microbes, dander, and such, would get filled with paint and plug up too quickly. Here you can also see the duct tape I applied around all the cut edges to contain irritating fiberglass.
I also added bulb weatherstripping around the outside of the filter, under the theory it would make the booth more airtight. I'm not sure it was worth the effort. In trying to get the weatherstripping into the gaps I sometimes had to make the gaps larger, so I may have been working counter to my purpose.