Looks like a nice building, what are you using for intake air filtration because the inside of the booth will be negative pressure and all the air coming in will be outside air? How are you controlling your exhaust fan speed...you don't want to take out too much air movement or your paint could have problems with popping? One last Question, did you allow for a floor drain in the concrete, not a deal breaker but they are always handy?
The building looks great and I'm sure your paint work will be much cleaner than if you had build this booth in the metal and body work area. That was real good thinking on your part and will only help in minimizing any contamination.