What questions should I ask the Roofing Contractor?

The past year I notice that my ceiling was becoming stained when after it rained. This past storm was so bad, I had to put a container on the floor to catch the drips. So , I’ve decided to call a Roofing Contractor give me an estimate on a complete new roof. What should I ask? What should I tell him? What do I need to know before hand? I would truly appreciate any and all suggestion you can give me and I thank you in advance!!