The GPR assessment of buildings depends on the structure or part of the building studied. In this paper, three different case study are presented, all of them about old buildings that need to be restored or modified. The radar study objective was, in all cases, the detection of hidden targets or structural elements. The first case presents the study of some terraces in buildings in order to determine the structural elements and also to determine approximately the materials, previous to an important modification. The second case is based in the study of the ground underneath the building. Several structures that could affect to the further restoration were detected. The last case presents the study of floors in the different levels of a building, showing the changes in the structural elements that support the floors. All the examples demonstrate the ability of the method applied previous to the restoration projects.