Hi,
Thank you very much for your answers. The problem is I tried using Cutoff tool; I duplicated my object and then cut parts of it and merged them together. It looked good at the beginning but when I merge the rest of my object I have again the same problem, it merges everything. With right click menu I also couldnt find an option with which I would be able to combine parts of two object. In the picture I uploaded blue object is one combined object and red is an other separate object. Since I try to use 3d coat in architecture I need to be precise. I somehow try to do something like a labyrinth and tit should work as a corridor, so it should be one object but it shouldn't be combined more than once. I mean it is hard to explain but I need to combine those objects only in one of the intersection not in every intersecting area. since it needs to be a building at the end I need to have one combined shape that intersects. So unfortunately cutoff tool works only if I cut my model to more pieces which does not allow me to have one combined mesh. As I tried to do it with the split tool it works pretty much like cutoff tool. It works only if I divide my model in to separate layers. I tried doing it with separated models too but then it becomes a great hassle to merge vertices in Maya. Since I cut my model and render as a section model I always see an extra wall, which does not make much sense. But thank you very much for your answers.