This is becoming more and more the norm as most businesses struggle with cash flow and the fact of being knocked(not paid for completion.)
I would suggest if you agree with this to at least find out where the company trades from.
Total roofing care.
I would advise you to only pay up to 20% of the overall cost to cover the tradesman's tools and travel costs.
I hope this helps. If you need any help negotiating with the tradesman, please feel free to give our customer care team a ring on 0207-198-8500 (Mon to Fri, 9-6) as they'll be more than happy to help you.