Why did I not think of that today Terry! I've been in 3 builder's merchants today buying roof insulation materials. I will go on Friday and ask. My builder hasn't really heard of it. He said they just put a wooden bead around the corners. That's not the style we are looking for so I will do a bit more research...
France Materiaux, Gedimat, Point P or Union Materiaux
Let's see if one of them can help me...unless anyone knows a specialist french plastering shop online?