Indoor Location-based Services (I-LBS) provide information that is compiled by taking into account the current locations of targets as well as models of surrounding buildings. Beside navigation applications there are lots of other examples on the field of workflow optimization or logistics. A key role among the value chain of I-LBS is a location model provider that delivers topological and geometric information about a building. This includes for example computing the walking distance between two locations, finding certain points of interest or looking up the room name for a target's coordinate, which has been measured by an arbitrary indoor positioning system. Building models have already been studied in the past. However, existing approaches focus either on the visualization of a building or they are intended to support architects in the process of constructing the building. In this paper we identify requirements for future I-LBS and we present a new location model that allows to store both topological and geometric properties of buildings. The model is specified as an application schema for the Geography Markup Language (GML). It enables a location model provider to utilize automatically generated waypoint graphs that can be individually adapted to the requirements of the specific I-LBS. Further more the waypoint graphs can easily be replaced leaving the remaining geometrical and topological properties unchanged. The feasibility of the model for I-LBS as well as different approaches for automated model generation are also demonstrated by a working prototype.