3D Indoor space topology, mainly referred as floor layouts and navigation routes, is the foundation of indoor Location-based Services (LBS), such as navigation in large shopping malls or interchange in large transport stations. Manually generating this topology is highly time-consuming, less cost effective, and prone to errors. This research adopts 3-D GIS technology and proposes a novel workflow to automatically generate the indoor space topology based on 3D building models in a format of Industry Foundation Classes (IFC). Floor layouts and paths including stairs will be identified and generated in the environment of ESRI ArcScene, a 3-D GIS software. Several categories of navigation routes are defined and constructed by a collective algorithm called i-GIT. This paper demonstrates the entire workflow and concepts to produce floor layouts and navigation routes using a 3-story commercial building model. More details related to i-GIT as well as their validation based on real buildings will be revealed in an upcoming article.