The depth of a bench will vary by half the amount of members we have on here.
When I built my one set of benches, I built them at 32" which to me seemed ideal at the time. My last set, I covered in laminated countertops which are factory made at 24". Not quite deep enough. To me, 36" is nice, but too deep, and 3' out from the wall takes up quite a bit of real estate. So in my mind, 30"-32" out is about right.
Now the height......there is no standard in a garage. Grab your favorite stool to sit on, decide where your arms would feel comfortable laying, then write that figure down. Next, stand up, and see what height feels comfortable to you for a working height. Alter the stool height to match the standing height, and make the bench top at that height.
Basically, it all boils down to what you feel comfortable with. Standing, sitting, reaching.......what feels good. I've probably had three sets of benches since I've had my garage, and 32" deep and 36" high is about right for me. I'm right at 5'11", and that is what I feel comfortable with. Taller or shorter would alter from those dimensions.
Good luck, and post up some pics when you are building them and when completed. Just start a build thread on them.
