Here's my home built booth. It has a downdraft squirrel cage fan, outside vent, and I use cheap furnace filters at the base of the booth, over the fan. I have no issues with airflow. I use spray cans in here all the time. It's hard on the filter, but there is no smell in the room at all.
The downdraft pulls the paint and dust down. I felt this was the best for me, seeing as I generally paint from an angle above and to the right. I thought rear draft might pull dust across the model and might also pull paint from the brush to the rear away from the model.
The inside is painted gloss white with under cabinet lights mounted at top. I later added a gooseneck reading lamp attached to the top for more light.
There is a clear acrylic door held closed with a magnet. After painting I can leave the model in there to dry, protected from dust and accidents.
Under the baking rack is a cheap furnace filter and a large square plenum area under it. It pulls enough air to use a spray can in there without any paint smell in the room, but that will foul the filter quickly. Luckily they are cheap and very easy to replace.
Here's the 400CFM squirrel cage fan on the bottom under the plenum.
It exhausts out the window. There is a dryer vent on the outside that closes automatically when the fan is off.
Blower and light switches. Low cost hardware store compressor with 5gal air tank underneath.
I was later able to fit plastic storage drawers between the switches for pipettes, neoprene, gloves, Q-tips, and various other things I use while painting.
Edited by dmk, 06 December 2012 - 07:25 AM.