Have you a written detailed list, that states exactly what you want done?
Do both quotes check out against your list?
If you leave the choice of product to the builder you may not get what you expect.
One thing that is very important is insulation.
Roofs tend to get very hot in summer (mine was 48C yesterday) and very cold in winter. In London, they will also pick up the noise from miles away, aircraft and trains.
You must decide how the builder will deal with these issues, the difference may well raise the cost of using the loft and spoil the use of the loft.
Also there are the matters of wind proofing and waterproofing, then maintenance. Maintenance involving health and safety these days calls for expensive scaffolding for the most minor process. A carefully constructed roof will save you money.
DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!