First tag the whole building without any "part". Therefore, building:levels, height refers to the maximum level and maximum height of the building, not an average. If a single closed way is enough to draw a building, you don't need multipolygon at this time. For nearly all applications that don't use "part", only those tag will be used.
Then you can add "parts" to better describe the differences in level, shape, height, color, type of roof of the different parts of the buildings. Those tags will only be used by applications that understand/use "parts". _______________________________________________ Tagging mailing list Tagging@openstreetmap.org https://lists.openstreetmap.org/listinfo/tagging
