Where we live a 'metal shop' adds ALOT to the value because everyone wants one!. We currently own and paid $50k Cash for a 30x60 x18 That's concrete, building, insulation, RV Door and underground electricity to just name a few small details.
One might argue its not livable space, but I know I'm out there everyday!!! :-) Mainly because we are building a 900 Sq ft, 2 story Guest Quarters (all permitted and they get you coming and going for the permits.)
Build it for yourself and always do it by the book for resale purposes!!!!
Apache Junction, Arizona