Hello Map47, Thanks for the reply. Your link is clear. If I understand correctly not a single edge should be inner and outer at the same time? What I did at
https://www.openstreetmap.org/way/354322295   is than also not good because I should trace around the building. What I did at Anderhalbacherstrasse 24 is than better but that does not require a multipolygon. Right? I did not get any warning of OSM and I am not familiar with OSMI but I will change it around Feutersoey. 
