Home Owner paying for materials

For a small job I'm working on in Cocoa, The Home Owner & I agreed to a total dollar value, or contract value, for the project, while allowing the Owner to purchase materials on his credit cards. Progress billing will cover my labor costs, and any incedential materials costs I pick up along the way. The final payment, or "job 100% complete" billing will be calculated after all job costs are accounted for and should come very close to being approx. 10% of the contract value. Being close to 10% of the contract value is a desired end result and can be achieved by coordinating the progress draws with the timing of the Owner's materials purchases.