The actual stations (frequencies, locations, etc) can be added using AFCAD by Lee Swordy, which can edit nearly every aspect of an airports facilities data.  I cannot, however, add buildings or things of that nature.  It adds runway textures and taxiway markings and things, but only as parts of the ground stuff.  For adding any sorts of buildings and things (including the visual model for the VOR station) I would recommend either EZ Scenery (payware), or Runway 12 (freeware).  EZ Scenery is by far the more powerful tool, but it costs money, and that is sometimes just not gonna cut it for a few FSers.  These two tools will both assist you in placing an object such as the station for VORs, etc.  Takes a bit of getting used to, but is well worth the effort.