When I make quilts for people I ask them some questions, First is there a theme or color. Then boy or girl, man woman? Baby or bed size? I get to choose the pattern of the quilt using the parameters set down. We can go shopping together or trust me to do it. I will say most people are afraid of fabric shops and when they see the cost it scares them away.
You MUST get a down payment for the fabric cost, including thread, batting and backing.
When you look at a pattern there is a material list. Add the total yardage up and set an average price for the cost of fabric per yard. In my area it runs from 7.00 to 15.00 so I split the difference and charge 11.00 bucks per yard. Times this by the # of yards in the quilt. Get this payment before you start the project.
Then you have to figure your time which is totally up to you to decide what you are worth and keep track of the # of hours you spend on the quilt. Patterns can be simple or complex so they take different amount of time which can only be averaged. Then the cost of quilting a simple pattern is usually done by the inch which varies around the country.
Write up an estimate sheet with all the specs on it. Have the person understand it is an estimate and the price my vary by 10 to 12 percent. Have them sign it. This is a contract and protect you from those who might change their mind after you finish a project.
There is a lot more to learn but these are basics that I use when doing contracted work. Always remember you are creating a work of art not just a quilt and you should treat yourself like an artist who gets commissioned to do a project.
Good luck with your quilting and keep on enjoying it!
peace