mux4
I was wondering because of http://wiki.openstreetmap.org/wiki/Key:entrance which say: "The entrance node should be placed on the building/area's way (i.e. its outline)."
And on http://wiki.openstreetmap.org/wiki/Buildings we can read "When tracing from aerial imagery try to estimate the place where the building position on the ground which may be offset from the roof-line as shown by the imagery on the far side given that images are normally taken from an angle." and "Differing from the ideal of mapping the outline of a building on the ground, many objects with building=* include parts of buildings (for example constructed on piers) which are only covering areas. building=roof and building=bridge even describe buildings which have, except its piers, no outline on the ground."