Mine is 22x40 with double 11 foot doors that open to each side. The overhead clearance is 14 ft with a peak of 17ft. The floor is a 8 inches of cement over sand and has a 3 inch drop in the 40 ft for drainage. The floor extends 30 feet past the doors giving me a 30 ft slab for washing the fiver and truck. I have 50 amp service. I do have a refer and all my shop equipment in there, but if I had to do it over I would go a little wider. I have portable heat, but very seldom turn it on and I have never winterized due to our climate. In my honest opinion I would go as big as you can afford. Good luck on your project.
RT