Did this myself many years ago, make sure you wear a breathing mask, that will stop the paint getting into your lungs but you may still get a bit drunk on the fumes. I used a small steel garage we had built for this purpose, just sealed up windows and especially over head so that nothing over head floated down. I also dampened down the concrete floor to keep dust from being blown up when spraying the lower areas. Before starting I made sure garage and panels were warm because little bubbles seem to appear a few months later if you don't. Hope this helps 
David
I found a hood at my local paint store that seems to seal up nicely under the "throw away" jump suits they have. Then there is a filter unit that you wear on a belt and hook shop air to. This filter has a regulator that will let you pressurize the hood. I've seen guys in the high end paint booths wear this stuff and it's OSHA certified for what that's worth.
A tube, I'm thinking something like what vinyl flooring comes on, with numerous holes on either side slid under the car & attached to a plenum that would have a filter & a blower of a design that the ventilated air would not come in contact with the motor then discharging into the atmosphere with a fine mist of water to keep the odors down for the neighbors sake.
I think your idea has some merit.
Controversely I've read a lot of people arguing wetting the floor. Claiming that the humidity causes the final product to look dirty due to paint "clumping" between the gun and the surface. I suppose there could be some truth to that, but I would think that if air is flowing properly it wouldn't be an issue.
I plan to have 3 fans pushing air in and 2 pulling air out. This will pressurize the the booth just slightly, enough to keep any dirt from coming in any small leaks that exist. In a professional booth this isn't an issue since its designed to be air tight. I forget the details now but my paint store also had some fancy filters they tried to sell me, I don't know if they are better than a nice furnace filter or not, but they are supposed to help eliminate the fire hazzard.
Something else I've read that seems to be in aggreance among many is the use of endust on the walls, your clothes, and even the car. Rumor on the street is that it's an anti static that doesn't leave a residue so there's no harm in using it. I think i'll stick with the PPG product on the surface on the car.
Jason
