I've got a 9x21' room that is divided as darkroom and finishing room. It is in the house and was a sleeping porch long ago. Problem is the low ceiling, about 7' max.
Building a new darkroom/finishing room in an outbuilding. That darkroom has 7.5' ceiling and is 9x12'. Finishing room has cathedral ceiling from 10' to 16' and is one side of a 12x18' room. It was all framed 3 years ago, but the county seems to think we need a permit. Go figure.