I kind of want to piggy back on this thread as well as your comments.
I have an attached, but detached garage that we were thinking of building the 2nd story on to make into a garage efficiency/1 bdr apartment for MiL. Now, I can use numbers to get ballpark thoughts on prices, but even those are wild guesses. And the numbers I can use ($120-$150+ sq/ft) are for detached garage apartments; mine would be attached.
Since I live in the CoH, I know things will have to change. But the changes will change the costs, which, I think, would destroy any estimates I have.
How can I ensure the builder A) knows what they'll have to do to comply with permits, B) get it done right the first time (I don't mind paying a little extra to ensure it is done on schedule and on time vs. paying 1.5x times and 3-6 months late), C) no unexpected problems down the road ("whoops, forgot to tell you that you need a new electrical panel, give me $3k more!) and D) will finish the project in some semblance of an agreed upon timeline.
I have some ideas of costs, but the biggest unknown (and the biggest preventer of moving forward) is what I would have to do to the rest of my house for permitting, as I want to connect the 2 living areas. But I don't want to waste a contractor's time by bringing them out, nor do I want to waste my time having someone who says they could do it, but when I start asking the above questions, I get
~egon