Hallo santasa,

the building multipolygons created were invalid in terms of data, as the buildings consist of parts glued together. At the very least, the relations should have been checked with a validator when they were created, then this would have been noticed. Since the OSM standard page does not support 3D rendering, great importance should be placed on correctness.

At https://www.openstreetmap.org/relation/17674019 I only removed the building tag from the relation. After all, the outer ring is not the building, but only the building itself with another inner ring. So the relation as it is now is wrong again. The boundary is only the outer ring, which includes everything inside. The inner parts, the important ones, namely the buildings, are excluded from the area by cutting them out as "inner". These are completely normal basics.

I found https://wiki.openstreetmap.org/wiki/Tag:boundary%3Dprotected_area#Social-protected-area, specifically protect_class=22. Sorry, I was probably too hasty. But remember: an outline in the relation is correct, everything inside belongs to the area and must not be cut out with inner members, but "outer" role on inner elements is completely wrong (hence the conversion to multipolygons with removal of the wrong members). Actually, multipolygons are technically the same as boundaries.

Best regards,
Mario