I built mine 15 years ago. I had a permit for 24 by 48 by 9 feet high, but I ended up building it 24 by 36 by 9. If I had it to do again I would have built it 48 feet long in the beginning as my access to the back for further construction is limited, although I'm still considering adding the extra 12 feet. I also would have made it at least 10 feet high to accommodate a low overhead lift. Mine is 2 by 6 wooden frame on concrete slab, which has been fine, no issues. It's wired for 110 and 220. Initially I had two industrial electric heaters but the cost of operation was too high. Last year I put in a single mini-split heat pump and it has solved all of my heating, cooling and humidity problems. I highly recommend this type of heating system and am considering putting it in my house as well.  

Updated drawings:

I had them put both doors to the right and the man door on the left wall at the back thinking that the area in the left side of the shop could be partitioned off to be a work room or office.