We report two novel aspects relating to the growth of oriented 3D arrays of SnO2 nanorods, based on the "purpose-built materials" (PBM) strategy. Under controlled conditions, the substrate acted as a topographic template and the growth direction of the 3D arrays of SnO2 nanorods was unrelated to the crystallographic characteristic of the substrate. A growth process based on the oriented attachment mechanism was proposed to explain this behavior, and this findings, reported here for SnO2, can be extended to include other metal oxides.