Basically, there are three types of structural roof systems: standard trussed roof, attic trussed roof and the cassette system.
Standard roof trusses are by far the most popular, but they don’t allow you to have a ‘room in the roof’ and only offer a small area of loft space for storage.
Attic trusses are designed to give additional space in the roof. They are designed in such a way that they remove the need to diagonal timber braces leaving a large ‘hole’ in the middle that can easily be converted to a room (or rooms). If you’ve ever seen new builds with roof lights installed, chances are they were built with attic trusses.
Roof cassettes are pre-fabricated sections of roof that contain insulation. They come into their own on large scale developments as they are quick to install. However, quite often they prove to be very expensive for one-off projects and rarely provide better thermal performance than standard roof construction.