I know that there are other threads about charging to make things for others. Sorry if this is a repeat.
A friend of mine told me that if she sells a purse (or perhaps a
certain purse I am not sure ) and provides the fabric that she
has she charges $40.00. If someone wants a specific color
or fabrics then she has them buy the fabric and still charges the
same amount.
How do you charge for this situation?

This is a very good question. I look forward to the responses.

I suppose it would depend on if it were a friend or just a person wanting you to sew for them (customer).

Keep in mind that your time/talent is worth something and your pattern and thread cost you too. Then there is your electricity and anything they forgot but is a part of the construction basics. Like maybe magnetic closures, fleece or batting, interfacing, d rings, handles, whatever.

I am thinking that the forty dollars she originally charged was broken down into all these supplies and her time. I would subtract for anything she bought/brought and charge the remainder of the balance for my work and supplies. After all she was happy with the price she was asking for the one that everything had to be bought and shopped for.

Interesting...