My builder says he will include the roof as part of the project - is that OK?

Roofing is a specialist job and general builders may not have the expertise to do the job properly. House extensions are significant projects and if the roof fails, the results can be catastrophic.  

It really is worth making sure you use a suitably qualified contractor. Use a Redland Select member and you can be sure that the materials and workmanship will both be up to scratch.