A very interesting subject for me us as we have just purchased a building plot and have the mad idea of not only designing our own house but also of building it ! As far as I can work out the best method is to get a planning application form from the local mayor and check through what is required on the form- a set of 4 or 5 forms has to be completed (all identical). These forms appear to be of national issue so shoudl be the same requirement wherever you are. A major consideration would appear to be the exterior appearance, well for us it is as we will live in an old village, which as I understand must be approved by a department in Paris, I think called Batiment de France.