I will only do this if I am bidding a very simple rough framing job. I would never do this as a general contractor. Too many variables and things you wont even think of til later. Framing is my specialty, as I have done it almost exclusively for 25 years, so I feel comfortable giving a firm price on the most basic house. As a GC, I like to meet with homeowners, discuss possibilities, take lots of pictures of existing, and then crunch the numbers. I do like to get back to them ASAP but sometimes 24 hours is not enough time to even give them a "ballpark" I think if the job is completed with no changes, (like that would ever happen) the final price should be within 10% of the original ballpark price. Its nice to set the ballpark a little high, as this will give you an idea as to how serious the client is. First meeting is also a good time to find out how they are going to finance the project. If the financing is uncertain, the project is not going to happen regardless of the price.