Go onto the Lewisham planning portal and see what has been done by others; its really useful and helped us a great deal when we extended both the loft (six years ago) then the kitchen last year We live in a half house in Bovill Road SE23 where around 50% have gone upwards; the majority have been handled by Central London Lofts who seem to do a decent job at a reasonable price. Our (front door) neighbours went down this route and there was relatively little disruption for us with the exception of scaffolding. We went down a much more complicated route as we wanted a very different look from the standard and had a full roof covered scaffold; this was more disruptive to the neighbours but they were fantastic as we kept them informed all the way. Consider having a chat with your immediate neighbour and see if they are planning a similar build; if so it may be an option to consider a shared steel down the (dividing non-load bearing) wall from which you can both build off. This may be a sweetener for the neighbour too One other thing we did was chat to neighbours who had already extended upwards and if possible have a look to see how they did it (difficult ATM). To finish it really is well worth doing; we absolutely love the space Hope this helps a bit and feel free to pm me if i can help more Good luck
