I know it sounds ridiculous and is frankly, dull.
We live mid terrace and originally they were all two up two down. If you stand at the back and look at them they all have single storey bathroom/kitchen extensions but with various roofing. Ours is flat and felted, next door one way is flat and fibre glass something or other, the other side is a tiles, sloped affair. It looks pretty obvious who owns which roof as they extend from the relevant house. Annoyingly, the actual extensions are not so simple. Our extension is L-shaped and the I part is covered by our flat roof. The _ part is under next door's tiled roof which also covers her kitchen, hall and bathroom.
The problem is that her roof is leaking substantially and we are having problems in our kitchen. So who has responsibility for the roof? The deeds don't say and when we moved in we had to get an indemnity policy for rear access as who owns what wrt the yard at the back was never established despite extensive searching. We are happy to go halves or something if it stops the water running down the kitchen wall and into my plug sockets. The snow has really exacerbated the problem. The woman next door, who is a landlady btw and living a long way away now, is aware of the problem but hasn't fixed the roof. So if she refuses, is there any clear way of establishing who owns what?
Is everybody asleep. See, dull.