The disclosed subject matter relates to computer implemented methods for generating an exterior geometry of a building based on a corresponding collection of interior geometry. In one aspect, a method includes receiving a collection of interior geometry data of a building. The interior geometry data of the building corresponds to one or more levels. Each of the level(s) is associated with a corresponding vertical span, and to one or more 2-D section polygons. The method further includes extruding the 2-D section polygons into 2.5-D section polygons, by assigning to each of the 2-D section polygons, the vertical span associated with the level(s) to which the 2-D section polygons correspond. The method further includes constructing a 2.5-D merged polygon set based on the extruded 2.5-D section polygons. The outer shell of the 2.5-D merged polygon set corresponds to an exterior geometry corresponding to the building.