I have decided that the best use of the loft space is to have a 5 metre side dormer, which will create the main bedroom area. The ensuite will be within the non-dormer space to the front and the other room (probably office / spare room) will be the main side area (top in the drawing), which is wider.
If all goes according to plan, building starts in September 2015, just after the kids go back to school.
A plan: The bold horizontal line marks one of the steels in the apex of main room, the vertical dashed line in the apex of the study room and the dashed angled lines are the roof valleys. The flat roof will have a fibreglass roof cover and the ensuite will have a roof window – the architect missed that off! New stairs above old stairs, and there should be another roof light above them. The only normal window is in the rear gable (left of photo) that will look into our back garden. This is also the fire escape!
The ensuite in this area:
The Spare room / study in this area:
This area only requires two supporting floor steels to support the roof, rather than a beam along the apex.