All I can say for now is figure out exactly what all will be going into you shop. Draw it out, lay it out, map it out, or whatever. Than add about 20% for extra storage and wife's things. Then when you are certain of the shop size you want, add about another 10% to be safe. Make a photo copy of your rough drawing and give to your builder showing him exactly what you want. OH YEAH, when you are making your photo copy, make sure you adjust it to about 400%!!! You can never be big enough, and not doinog it right from the beginning SUCKS! I tried cutting corners, saving money, etc. Well I saved money, but I am already looking into adding on, building another, or something. It's only been 3 years.