Quote from laminutederireI can tell and I knew.
It wasn't bound to one nation but to one region, because at that time, what matters the most was resources. You wasn't able to get rocks or woods from too far apart in great quantities, so you had to do what you can with what you had, and that led to choices that made part of the style of buildings. In addition, architects weren't the most important people there, the one with real powers in the decision were those who ordered the building and those who built it.
Which castles have you been visiting?
Yes of course, though limestone and granite are common in both Germany and France. We're talking neighbouring countries with comparative geology. Fact of the matter remains that castles in both France and Germany share aesthetic traits and materials, and that build times would sometimes prolong resulting in different styles. The Mansard roof of Scepter is commonplace all across Europe for instance. Just like you suggest, the person who pays for the castle is ultimately the one who decides in which style to build, meaning they could build whatever they like.
I haven't visited any castles outside of my home country. Internet studies are adequate.