CedB12
I think the footway that you point out should be tagged footway=colonnade as described here in the wiki and as used in the Forum building just north-east of the BC building: https://wiki.openstreetmap.org/wiki/Key:covered#covered.3Dcolonnade

I don't have enough knowledge of building mapping, but at least that wiki page seems to contradict the idea that buildings should be mapped according to the ground floor only.

(Note for anyone else reading this: this building does extend that far when you consider the floors above. It is not simply a roof overhang.)