Procedural Content Generation can help game developers by automating the creation of content that is costly and tedious to develop by hand. We present a system to generate 3D game levels based on interior spaces such as buildings and dungeons. Our system generates individual rooms by using a shape grammar to recursively subdivide rectangular blocks. Multiple rooms can be joined to form a larger level layout. Our system searches for a good layout based on a fitness function specified by a human designer. We tested three search algorithms for this purpose and found that in almost all cases an evolutionary algorithm produced the best results. Once a level layout has been selected, architectural details are added to the layout by placing modular meshes such as columns and wall segments. The final level can be loaded in Unreal Engine 4, a widely used game engine.