I design my level interiors in Wings3D, but the same questions would apply to any 3d designer. When you design your scary complexes and starship interiors, do you import them as one giant unit (the walls, ceilings and floors, not the decor), or do you import floors, wall segments, and ceilings and glue them all together in unity? I tend to map out the whole level in my designer, and import it - the drawback being that if I need o add a room, I have to reimport and reapply all the materials every time. Also, there may be some issue with the renderer where the culling function may feel the need to keep the whole object in memory the whole time, wasting resources. If the answer is to design rooms one at a time, or even wall segments, floor segments, and ceiling segments, but then how do I attach everything so there are no coincident surfaces and/or gaps? I would love it if I could include in my geometry an invisible null object at the center of each door and had a script to snap the parts together.