hey,
Ive remapped a building that consists of multiple parts which each have a different number of levels: Changeset: 168795517 | OpenStreetMap. I added each part as a separate polygon tagged with building:part, created an outline and added everything to an relation. As this is my first time using the building:part I would appreciate if someone could give me some feedback on how it is mapped. And yes I studied the wiki entries for building and building:part 
thanks!
You deleted two buildings that had different housenumbers and replaced them with one building with both housenumbers: addr:housenumber=8a;8b
Now the information about which part is 8a and which part is 8b is lost. Also it would have been nice too re-use and change those buildings to building parts in order to keep the history.
The building tags should go to the building=yes area, not the type=building relation (also in this case a type=building relation doesn’t seem necessary¹):
This outline must be tagged with
building=*. The outline also holds any other tags (e.g. address, name, overall height, operator, …) which apply to the building as a whole.
Why the building has min_level=1?
unless at least one part of a building is hanging over the building footprint, or the building has a complex structure with lots of parts, one can simply position building parts within a building outline as described in Simple 3D Buildings.
@ivanbranco Thanks for your answer!
Your right. This is because the information about the house numbers was wrong. I’ve attached an image that I got from the property management, that shows the overall situation (building heights and house numbers). The dashed lines mark the border between 8a and 8b. So the middle part of the building has one height, but belongs to two different house numbers. I was not sure, how to map this.
I’ll change this!
Because the numbering convention in this building starts with level = 1 for the ground floor. But after reading Simple Indoor Tagging - OpenStreetMap Wiki I’m not sure if I used min_level correct. The situation is the following:
How to tag this?
I guess only part of it is on stilts? In such case you could map building parts as this (pardon my poor drawing skills):
Blue = building:level=1
Red = building:min_level=1 + building:levels=x
Only relevant for indoor mapping but not for buildings themselves (building:levels is about the total floors, not how they’re signed).
This is a more valid usecase for building:min_level, especially if there is some actual reference like signed levels or nearby buildings.
Map the addresses separately as nodes placed inside the building outline, not on the building/building parts.
