I would put in something like this
Owner supplied materials.
Contractor shall not be responsible for the ordering, delivery, quality or fittness of any owner supplied materials. All owner supplied materials are to be on site available for contractors inspection prior to the start of construction. Any delays or additional work caused by defective or missing materials will be billed as an extra charge at the contractors usual hourly rate and may delay start or completion dates. Contractors only warranty is that any materials supplied by the owner are installed according to the manufacturers installation instructions in a workman like fashion according to code.