I just finished such a project. I bought an acre and a half, designed and built the new house (finished the house this past June and moved in), then finished off the remainder of the darkroom that I didn't do as part of the main construction (got all of the structural things done as part of construction including flooring, drywall, plumbing, electrical, vending, and painting), the rest I did afterwards (cabinets, sink, etc). Doing it that way minimized the budget creep after construction. The only other difference is I built my new dedicated darkroom and finishing area as part of the back basement. I'm also on well. You might read through the
Darkroom Portraits Part 2 thread - there a a few of us that have recently done the same and discussed various aspects of the projects and pictures along the way.
I bought a few darkroom books off of eBay cheap - they all pretty much cover the same basic layouts and considerations for wet-side/dry-side and other issues - nothing many of us ancients didn't know 50 years ago when I set up my very first darkroom, but was fun to review nevertheless. Today there are things one can improve upon from the days of old re: air filtering, dust control, venting, temp control, disposal, and so on. A lot of my expense beyond the structure went into convenience, comfort, and automation. Having had to live with sub-standard darkrooms all my life I wrote a complete list (plan) covering every aspect of darkroom problems and challenges I wanted solved with the new space before I even got started with construction and how I was going to solve each - and did. Did I make any mistakes along the way? Yup - it's inevitable even with the best planning, but they were minor and could be dealt with.
Regards,
Mike