I used to do a lot of home dec sewing for people, window treatments, duvets, etc. I told them how much yardage they would need, and had them buy the fabric and any other necessary supplies. I always supplied the thread because I use high quality thread. I couldn't tell you how many people changed their mind about the project when the found out how much the fabric was going to cost, plus my labor. I made a generous estimate of time it would take and then gave them a cost of the labor.
As far as making quilts to sell, I don't. It is too hard to put an estimate on the time it will take, plus I would end up having to charge about $.05 an hour to make the cost something a customer would pay. No, I make my quilts for gifts and for charity.