In answer to some of the questions, yes it is being done under building control.
The BCO is happy with the work done so far, including the brickwork, lintels etc.
I was just looking for ideas in working out how to fit the roof in to the existing setup. Some forum members have given me enough helpful advice to push me in the right direction. The "you've not got a clue, grab the popcorn etc" crowd, not so helpful but then I guess they don't know my situation so I'm not offended!
Thanks again Ree for useful help. The ivy is coming off when I get time. Under the sand is the compacted hardcore. Once I decide on which flooring to use (and therefore the thickness of slab) I'll lay the DPM, lap it up the walls higher than the DPC and lay the concrete slab. The rest of the house has concrete floors.
I am thinking that the best course of action is to move the soil stack in line with the toilet outlet will get rid of the horizontal pipe and allow a much greater flexibility in the height the roof can abut the wall.
The bricks on the top of the party wall are crumbling and I might be in the position, with the neighbour's agreement, to remove them and the tile layer and build the wall up a bit and finish it off with some coping or saddle, at a high enough level to allow me to flash my roof into.
Does that seem like the best solution?