Things are moving right along with our daughters house. They have a contract on a house in Falls Church, Va with a 1 acre lot. The house has kind of an ordinary 2 car detached garage. We broached the subject of replacing that with a carriage house for us upstairs (and a 1200 sq ft shop in the basement) and they jumped at the idea. Of course there are a hundred potential obstacles.

Aside from zoning issues, the first thing that comes to my mind is how much it would cost us to build what I have in mind.

I am looking for advice as to who to approach and what sorts of questions I can ask to get a rough construction estimate.

In case someone here has the smarts to help me directly, here are some basics:

1. URL to some online plans that are very close. http://www.thehouseplanshop.com/053g-0002.php The big modification is that I want to use spancrete and create a basement.
2. We would be willing to do some painting and finish work.
3. The cost of the land is $0. We would demolish the existing 2 car garage and replace it with the carriage house.

ideas?