I would be concerned if the person who did the roofing work refuses to provide you with the requested insurance policy. If you have concerns that the roofer is not a licensed roofer, you might look him or her up online with your state's contractor's licensing board.In California, if a person who is not a licensed contractor performs work requiring a contractor's license, the unlicensed worker cannot bring a lawsuit for money owed. This may be the case in your state. If so, you are entirely justified in holding back the money based upon documentation being provided to you as stated in your question.If you have a written sub-contract for the work of the subcontractor, I would carefully read it to see what duties are required by him or her about providing you insurance information. From what you have written, it seems you are justified in holding back the money.