OK so after much heavy rain overnight I discovered a stain on the ceiling that is directly under a dormer window in the room above. After a 7am excursion into the roof space around the back of the dormer I am pretty sure I have traced the stain source. Following the water source is not so easy.  From outside I can see a lot of moss built up on the roof and worse, along the flashing itself.  My first plan when it stops raining is to try to clear the moss on the roof, starting specifical