Bill,
It's probably worth telling people what you are planning to paint (so we understand what you mean by "small paint booth" and also whether this is a paint booth for one time use or for frequent long term use. Are you painting for show quality, or driver quality? What kind of spray equipment are you using? (certain types create less overspray than others and require less ventilation.)
Through thirty years, I've painted lots of driver quality cars and parts without any fan or filters at all, both in the driveway and in the garage. Back when I worked at a body shop, we often did small jobs right out on the shop floor, without bothering to move the parts into the booth. It requires careful cleaning and removal of anything from a garage that might be affected by overspray.
Like you, though, I have plans to build myself a permanent paint booth for more frequent use and less cleaning hassle. I'm all ears too if people have suggestions for a home spray booth, though I'm thinking 14 by 24 to fit full size cars. May as well go whole hog and install filters and a fan in a dedicated booth, though I intend to go on using HVLP equipment, which creates far less mist and overspray than the old siphon guns I learned on.
