In this report monostatic and bistatic 3D SAR imaging of building interiors are studied and compared. The work is based on computations made with physical optics in combination with transmitted physical optics, geometrical optics and transmitted geometrical optics. The bistatic geometries correspond to a fixed transmitter position and a variable receiver position in elevation and azimuth. The calculations have been made at UHF-band 0.3-3 GHz, HH-polarisation. The imaged building is a two-storey seven room building placed on a smooth dielectric ground surface. The results show major differences between the monostatic and bistatic building images. In the monostatic case the walls are imaged as lines, while in the bistatic, due to ground interaction effects, walls are imaged as surfaces. In 3D SAR-imaging the forward scattering sector can also be used for mapping building interior. For imaging of building interiors frequencies > 0.2 GHz should be used if the outer walls consist of reinforced concrete. At lower frequencies the electromagnetic wave will be strongly attenuated due to the metal lattice structure of the steel rods.