I've got an entire city in Microstation DGN format. I'm able to convert it into Google Earth (KML), DXF, SVG and other formats, and then in .osm with ogr2osm.
However, the 3D model is build entirely with wireframes (triangulated polygon strings).
This does not seem suitable for .OSM.
Does anyone have experience with such problems and is it possible, and will it solve it, to change the model from wireframes into solid surfaces or solid blocks.