It’s great that your builder is someone you trust and has a good reputation among friends and family. Saving 4-5K is definitely tempting, but roofing is a critical part of the property and even small mistakes can lead to costly water damage down the line. If he’s experienced with metal roofing specifically and can offer a warranty or guarantee on the work, it might be worth considering. Otherwise, I’d lean toward using a licensed roofing company—especially for peace of mind and potential resale value. Maybe get a written scope of work and see if he can match the roofing company’s standards.