text: I assume you mean landuse=grass in combination of an area? But this combination is completely doable, or rather the only one possible for landuse=grass and area.
  
  But once again, which landuse tag is more appropriate? Polygon is no sort of landuse!
  
  Yes, the building is part of the grass area but every good map renderer ( like the one of osm.org ) handles this with ease. You could also argue that every area ( building, parking, etc. ) located in residential area has to be cuted out! Where to begin and where to end?