Hi Veronique, Thanks great article, very useful. I have a small request if possible? Is it possible to edit Blog posts once they have been published? If yes then I would like to suggest a small change to the title so that it includes the word "Roof" as well as "Walls" and perhaps a suggested use that it might be useful for cutting skylights as well. I had been looking for a method to cut a skylight in a flat roof. I came across the later post on adding a window to a sloping roof but I seemed to overlook this post which is really what I needed. I came up with a similar solution and it was an worthwhile learning exercise so perhaps it was good for me anyway :-) Thanks Jonnie63