In this paper we present a low cost approach to automated reconstruction of 3D roof models which can be used for generation of a realistic 3D environment of an urban area in a virtual reality application. The key aspect of the method which differs from the other studies is that only one aerial view is used and architectural knowledge is introduced to form 3D roof models of buildings. First buildings in the aerial image are located using footprints of buildings in the digital cadastre map and roof image of each building is retrieved from the original image. The corresponding roof lines of the buildings are obtained by processing each roof image separately. Finally by merging 2D roof model and architectural knowledge about the building such as the building type and possible roof slope angles, 3D roof models are created.