Despite the large quantity of researches and publications achieved during the last three decades about 3D building modelling by using Lidar data, the question of inner roof plane boundaries modelling needs to be more extracted in detail. This paper focuses on detection and 2D modelling of building inner roof plane boundaries. This operation presents an imperative junction between roof planes detection and 3D building model generation. Therefore, it presents key procedure in data driven approaches. For achieving this purpose, roof boundaries are classified in four categories: outer building boundaries, inner roof plane boundaries, roof details (chimneys and windows) boundaries and boundaries related to non-detectable roof details. This paper concentrates on detection and modelling of inner roof plane boundaries and roof details (chimneys and windows) boundaries. Moreover, it details the modelling procedures step by step that is envisaged rarely in the literature. The proposed approach starts by analysing the adjacency relationship between roof planes. Then, the inner roof plane boundaries are detected. Finally, the junction relationships between boundaries are analysed before detecting the roof vertices. Once the 2D roof model is calculated, the visual deformations in addition to modelling accuracy are discussed.