I was right to have the jitters at the change of tack at the end of yesterday. This single frame idea is not going to work either. It will leave an odd sticking out bit inside (see picture). So that will have to come out. Good that I didn’t fix it.
I’ve now decided on a hybrid approach. I’m not going to move the existing rafters (the original plan). Moving the exising rafters was going to be really complicated as it would disturb the external brickwork. This is no longer an option anyway as I’ve cut them off! I’m now going to put new rafters in the right place. Watch this space!