[indyjps]

build as big as your lot will allow. it may seem like too much $ now but you'll always wished you added a few more feet. go as high as possible. if you cant do a two story try using a rat wall for height or get creative with the trusses to open up the ceiling area. i currently have a high ceiling that allowed me to build a loft for storage.
garagejunkies.net is a good site to check out.
sketch up your set up prior to wiring for welder, air compressor, parts washer, bench etc. add outlets in the ceiling for pulldown retractable cord reels ( saves tripping on extension cords) think about running air lines around walls or across ceiling for pulldown air lines.
good luck