been asked to do one but feck knows how easy or hard it will be
If its a glass roof, either do it first thing, or later on in the afternoon or evening, don't do it when its hot!
Just get the custie to move the furniture out, if its carpet i normally dust sheet the floor to catch any drips. If the glass sheets are quite large, i normally soap up and just do a straight line with the blade.
Then once finished, if its a tiled floor, i just run a mop over it.
Not hard work at all, its only hard work if its really hot.