I have a typical 200 year old 45 degree kent peg roof. I am fitting a
loft room, essentially insulating and plasterboarding the entire
triangular cross section (not bothering with knee walls) and a very
small ceiling. I want to keep it as a toblerone shaped room.

Half way down I have to build a stud wall to enclose an en suite
bathroom.

My question is, do I fit my 4x2 frame up and under the rafters to help
support or do I put my 4x2 frame alongside the rafters and fix my wall
to the rafters from the side.

Is there a preferred method? I'd like it to be strong and last and I
am a little worried that a roof that will flex with temperature and
winds will crack my paster, particularly at the corners where roof
plane meets stud wall for example.

jON