The complexity of describing buildings is immense and much work remains to be done. One needs to obtain a good understanding of the accuracy and reliability of a building’s key numbers in all cases. One needs to solve the problems faced when: parts of a building are occluded; the geometric resolution of the source data varies; buildings deviate from expected shapes in the event of add-ons and of complex footprints and roof shapes; the building’s use is mixed and an industrial use leads to windowless facades; cadastral detail contradicts image detail, etc.