The main purpose of the spray booth in the context of a water based coating is not to remove toxic fumes as much as it is to remove any overspray from the painted surface and the painter as well as provide a dust free environment so that the surface doesn't become contaminated.

Commercially available spray booths (a cross draft design is good) are a good option.

More on spray booths...

> spraybooths.com
> paint-booths.com

If you decide to build your own spray room, certain rules of thumb need to be followed.
 
The total volume of air flow can be calculated by taking the cross sectional area (not length) in square feet and multiplying by 100 to arrive at the CFM requirement. Ex. 8 ' by 10' would require 8,000 CFM.

With this arrangement the air flow would be drawn along the length of the booth, the piece being painted would be positioned between the painter and the exhaust. Even flow is important.
 

In the case where spray booths are drawing air from the inside of a building, there may be a requirement to introduce an air make up system, depending on how long the booth operates, and how large the space is.

Painting the floor within the spray booth is recommended.