Some time has passed. The discussion ended without a change. Ok. One addition to the relation of type=building: If you have a building of only one outline AND inside of that outline a smaller part of building being higher/lower, you tag it as 2 seperate lines. Be sure to add the tag "building=yes" AND "building:part=yes" to the outline! Else the kendzi3D plugin will not render the outline building.
Seen that problem in this area: http://osm.org/go/0I5UVEl8n-- I added the 3D outline of the houses, the trees and some small other changes. Now I wait for http://maps.osm2world.org/?zoom=16&lat=47.06307&lon=15.46166&layers=B00TTFF to render it ;-)
The time before I tried my hands on the "Herz Jesu Kirche" in Graz, but the simple 3D schema misses a lot for churches: http://osm.org/go/0Iz~o8jUH-- and http://maps.osm2world.org/?zoom=18&lat=47.06977&lon=15.45576&layers=BT0TTFFF Ok, the last link is not yet rendered with latest changes.
But I do miss: - roofs like gabled, but only one half (side area of church e.g.) - some material like sandstone