Great space, you'll love it!
We did almost exactly the same for the shop at was was then my Dad's place (now my brothers since he passed on). 40 by 60 with 12 foot side wall. We put in a concrete floor and divider wall in one end 20 feet deep - makes about a 3-car sized end garage. We added another concrete strip down one side 12 feet wide for an office and stationary machines (air compressor, saw, etc) with a mezzanine storgae area above that. We left the ramaining area gravel for storing tractors / skid loader etc.
This has been the "family shop" for everything you want to do in a shop for about 15 years.
