I second asking everyone you know for who they (or friends of theirs used) to make sure you get reliable answers.
I've never heard of negotiating with a contractor for a price. In my experience it's kind of been like paying someone to do your taxes, cut your hair, etc - what price they quote you is the price that you pay. That may vary by region though since I've never heard of it around here. If a contractor will do it with your materials or not will vary from contractor to contractor since many are given discounts on materials, usually 10% that I've heard, but will charge you the regular rate to have a higher profit.