Procedural generation of virtual worlds is an important aspect of game development since decades, typically for increasing replayability or for speeding up the level creation process. However, the utilization of this potential has always been a great challenge due to the difficult controllability of the underlying algorithms or limitations to specific level geometries, like 2D regular structures. In this paper, we present a novel approach for semi-automatic generation of a wide variety of 2D/3D corridor and room systems. The underlying processing pipeline is based on a separation between a user-guided generation of a graph-based abstract level structure and a fully-automatic construction of the corresponding geometry using a pre-modeled component library. The core algorithm is built on the computation of an extended minimal spanning tree, which can be controlled by a set of intuitive vertex and edge parameters. First experimental results have shown that our incremental generation pipeline allows the efficient creation of complex indoor levels, minimizing limitations on level and game designers' creativity.