Roof extension on flat roof over property boundary (double-brick shared wall?)

Questioner

My neighbours want to build a roof extension on the flat roof and have asked permission to place this on the double-brick boundary wall. This means that they move one stone beyond the heritage boundary. I don't have much of a problem with that, but I wonder if there are any disadvantages to it. Do I need to record something and have it signed? something like: holding the neighbors responsible for any consequential damage caused by the construction? How do I do that, is there a standard procedure/form for that?

Lawyer

You must also take into account that this will limit your own development options and those of any legal successor (buyer) of your home.