Build one 24" tall x 24" deep x 48" long. Or bigger if you want. Use two blowers. Don't worry about a partition, unless you really want one, just turn one blower on if that's all you need at the time and work in that side of the booth. Of course that means individual switches for the blowers. Use another for your lighting. Put doors on it so when you're finished painting you can leave what you just painted inside to dry/cure and you can close the doors when you aren't using the booth to keep it clean. Small fluorescent lights, such as under counter lights, are inexpensive, small and can be daisy chained together. Only problem is the availability of different types of bulbs. I just go with the standard bulbs. You can put them in the corners and across the top front and rear. You'll have plenty of light and few shadows. They aren't open fixtures, their self contained with covers over the bulbs. Don't use halogens, they put off a lot of heat. Use two 24x24 furnace filters in the rear. Sacrifice a couple inches at the rear of the booth so the filters aren't directly against the rear wall. That way your blowers can draw through most of the filter rather than just whatever size hole you put in the rear wall. Use a couple of strips of wood top and bottom in the booth to drop your filters in. Make the front bottom strip removable to make it easy to change filters. Build it out of heavy plywood and paint it white. At least on the inside. When the inside gets dirty from overspray, repaint it. Don't worry about lining it with tac paper, shelf paper or newspaper.
My booth is homemade. I gave a friend the dimensions and he put it together out of scraps he already had. He had the tools and enjoyed woodworking. I didn't. It's 18x18x18 inside. I was primarily an automotive modeler at the time. The top is a piece of Lexan. There's a little trap door on top to insert/remove the filter. I have fluorescent lights in the front corners and across the top. It has a door. I believe the blower is 275cfm and the booth is usually less than a foot from a window. It draws very well. I simply ran dryer hose to a dryer outlet mounted in a piece of heavy cardboard the width of the current window I'm using. Open the window, insert cardboard, close window. I rent and move from time to time so I haven't bothered to do anything other than that. I've been using this booth for 10 - 11 years now.
Yes, it's constructed from flammable materials and I keep small bottles of different thinners and cleaners inside of it. I haven't had a problem. It would be nice to build one from sheet aluminum but it would rattle, hum, vibrate more. You could have problems with static electricity and it would have to be(should be) grounded.
Tony