Welcome to OpenStreetMap!  Thank you for your contribution!

I suppose the problem here is that it depends on what software you're using whether you can add buildings.  If you have a desktop computer with a mouse you can look into browsing to openstreetmap.org and using the iD in-browser editor to draw a box that indicates the building, matching satellite imagery of the area (iD does not behave very well on phones/tablets IMHO).  I could not figure out how to easily do this with Vespucci even, perhaps just because of the limitations of the Android platform...