i am half way through building a bespoke bike store for my son at his place. The roof will be a single pitch made from 18mm OSB covered in felt. Perfectly happy using OSB in this situation, can't justify using decent (expensive!) marine ply. The issue I have is more one of finishing the job neatly. Where the roof butts up to the house I will need to make three cut outs to accommodate various downpipes. I can't really see how I can get the felt to look neat in these areas and would like to find some trim of some sort to tidy up the cut outs. I suppose in my mind the cut outs will look best if they mirror the shape of the pipes but I suppose they could be square - which I suppose would allow the use of right angle upvc channel or similar. Any thoughts? Ps I am aware that the edges of the OSB need to be sealed for best protection.