You can draw them with iD (take the tutorial) or import them from a open data source.   You could also use rapid https://rapideditor.org/edit#background=Bing&datasets=fbRoads,msBuildings&disable_features=boundaries&map=16.89/31.37329/-100.48596 to click to draw what they have found.  Otherwise there are too many buildings to add and as a general rule we close any note for requests to add buildings.