I had the same exact question as you back in April-ish. The "Search" feature is your friend. "Spray booth" and "Paint booth". Also "Google" for the same words. A basic entry level commercial spray booth about the size you want will cost $150-$250 shipped.
It will take at least one hour to read all the threads. You need to read all these to get a good background on what is and isn't out there. You will find mostly pictures, comments, suggestions, and theories rather than any specific well drawn out plans. I've gathered that a "shaded pole" or "squirrel cage " blower is much better and safer than kitchen hood fans, muffin (computer case) fans, box fans, shop vacs etc. Realisticly expect to spend $75-$200 if you build your own. Price depends on booth size and how much material you already have laying around. Biggest expense will be the blower.
Ask questions. People on this forum are very helpful.
Hint: If you find something you like "BOOKMARK" it. I wasted lots of time going back finding a thread of interest that I thought I would remember.