I assume you are going to build walls? [Linked Image]
I used to do my recording in a bedroom that was 10 by 13 feet by 8 feet high. I remember doing the calculations (which I forget how to do right now - duh)for room modes for that size, and the result was pretty good. The only thing you need to watch with a room that size is that it's just a little too small to reinforce the lowest bass frequencies really well, so you might have to do a little fiddling with speaker placement and bass traps to get your monitors to sound really good in there.
Everything Larry said is true; you'll have to isolate your work area from the garage door because garage doors let a lot of sound through.
Oh, you might think about building up the floor so that it's level, using a wood stud frame with a plywood top, fibreglas stuffed under the floor. I wish every day that my garage floor were level.

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Later,

Pat

[This message has been edited by Patrick Bryant (edited 09-15-2002).]

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