In this paper, we propose to investigate the joint use of high-resolution optical and SAR data, for building extraction and 3D reconstruction in large urban areas. A sequence of methods providing, in a semi-automatic way, the building detection and reconstruction is presented. Potential building footprints are first extracted on an optical image by a twophases process (coarse detection and boundaries refinement). The framework of fusion with SAR data is then developed. A first step of registration allows us to get a fine superposition of optical and SAR building features. Then, we show how to take benefit from the introduction of SAR data: The proposed methodology, based on the optimization of criteria refering to building SAR characteristics, allows us to simultaneously deal with the building presence validation and with the height retrieval.