I work for a mostly residential roofing company and we do emergency roof repairs as well as contracted work. For these emergency leak repairs we basically work on a time and materials basis ($150 per hour per man plus materials) not to exceed $1,200 for any given repair. Is there any particular document we should be sending them to get it in writing? We've had a few customers who were explained verbally but claimed not to be informed. Keep in mind the scope of work is mostly unknown until we get on the job-site. How can we send a contract when the scope of work is unknown?