SAR tomography is a powerful 3D reconstruction method. Nevertheless, in urban areas, results are usually rather sparse and some post-processing is needed to obtain 3D buildings. In this paper, external information about building footprints is introduced in the 3D reconstruction process. This is done by extending the recent method REDRESS based on a graphcut method (Rambour et al., Computer Vision and Image Understanding 2019). The graph construction is modified to take into account spatially variable weights depending on the footprints location. Experimental results show a clear improvement of the retrieved shapes.