Convert single skin outbuilding. Help.

[Infoelec]

Hi I want to convert a single skin outbuilding into a office / room, but I have one problem, the roof at the moment sits on top the neighbours double skin wall, I have no way to move the roof either side, so what's the solution?

Also id need to raise the roof as its only 1.6m! But to do this id need to build on the neighbours wall to raise it.

Preferably I wouldn't like to touch the neighbours wall or raise it.
All the walls are single skin expect the back wall which leans onto the neighbours.

Corrugated Roof
No DPM in floor
Airbricks are installed.

 

[noseall]

Dig your own footing, build a new wall and put your roof on this.

 

[Infoelec]

That is also an idea, for 2.5 mtr wall what's the footing depth? Also could I raise it by creating a wooden frame ontop of the neighbours wall?