Having looked at the 3D information inside OSM, it's actually much more advanced than can be handled with facades alone, e.g. The Fernsehturm in Berlin, consists of several cylinder buildings, which start at different levels (i.e. min-height tag). Since facades can be offset from the ground, the 3D effect falls over with buildings like this. The effect isn't bad, but it could be much much better. Additionally, other buildings have domed roofs, sharp roofs, etc, none of these can be rendered as a facade. After stabilising what's currently in the application, I might put it on the list for the program to actually generate a proper 3D model based on this information. The .obj file would just use a simple repeating texture, but it would still look much better than the default facades