Those options should be incorporated into the bids.
If you have him buy anything, expect that they will add markup.
I’m on the side of “sell it as is” and reflect tgat in the price or negotiate it in the sale.
My father got ripped off years ago by buying the materials and then paying the contractor for labor. The project dragged on way too long and went over budget.
Unless it’s someone you can personally trust my preference would be to get bids that cover the whole project.