I remember back in the time, maybe 3-4 years ago, Dupli-Color had a series of videos on an El Camino restoration project. At some point, they were showing how to build a paint booth in your own garage using 2x4's, plastic, fans and cheap furnace air filters
. If I am right, the ventilation was negative, this means the fans was pushing air outside the booth.
I was trying to find this back, but no success. Maybe this can give you an idea on how "not to" ruin the atmosphere of your garage permanently. I found this info very useful.
Edit: Found this on Blogspot: http://jessicombs-duplicolor.blogspot.ca/
If you scroll down on this page, you'll find the video I am talking about.