[Tagging] how to map simple buildings

[Martin Koppenhoefer]

I have just started mapping according to the simple building scheme and
have some questions to the more experienced mappers:

A situation I meet very often are buildings consisting in several parts,
e.g. often there are higher parts on the (flat) roof that are smaller than
the rest.

1. Which representation do you deem preferable:

1.1. map the largest horizontal building extension (e.g. building:levels=5)
and add on top a building:part with building:min_level=5, building:levels=1

1.2. map a polygon for only the part that has building:levels=5 leaving out
the higher part and add this higher part as building:levels=6 (no min_level
here).

1.3. Do you map these as building:part=* and add a third object (in the
simplest case) for the building with building=* to combine them? Do you
prefer the third object to be a relation or a closed way, and do you add
building:level tags as a fallback to it?


2. What is the "roof"? E.g. in the context of flat roofs which are
inhabited (apartments, terraces, etc.)
2.1. is this part of the "roof" and the level should not be counted in
building:levels (IMHO it is part of the roof):
http://www.dach1.at/wp-content/uploads/sl_dach.jpg

2.2 but if 2.1 is part of the "roof", shouldn't this also be 2+1 levels
rather than 3?
http://media.getrix.it/1/5544/2488638989.jpg

2.3 similarly, is this 5+1 or 6 levels?
https://imganuncios.mitula.net/casa_di_200_mq_a_collina_fleming_vigna_clara_roma_4010133485552255323.jpg

2.4 there are also cases where inclined tiles have been applicated later to
prefabricated houses with flat roofs to make them look more similar to
traditional houses. Inside the house has remained the same, but from the
street it now looks as if there was kind of inclined roof.


3. Am I right that this is not representable with the simple building model?
(It's a rotated roof, not parallel with the building sides)
http://www.cityastronomy.com/exterior-open.jpg


Thank you,
Martin
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