Hi Hans and Puybaret. @Hans, It seem I did not understand what you meant as subdividing my walls did not help at all. I've uploaded the unmodified version and hope I understand what you meant, when I see the modified file.
@Puybaret: Your "dirty" solution of multiple rooms (one big for the floor ...
I restarted using SH3D for planing windows. For an idea of these windows I created all walls and created rooms via double click. In two rooms the ceilings are fine but in two others they are very strange (see image attached).
I downloaded some 3d object and changed the texture.
When I insert the object I lose the texture settings. Look at the picture. http://img835.imageshack.us/img835/3816/texturebug.jpg
How I fix it?
Can I edit the texture setting - > mtl file?