// buildingFootprints represents the buildings that intersect the clicked parcel
var buildingFootprints = Intersects($feature, FeatureSetByName($map, "Building Footprints"));
var totalArea = 0;

// since a building may have multiple floors, we must multiply the floor area by the number
// of floors. Also note the building data shows some buildings in dense areas as crossing
// multiple polygons. To avoid miscalculation, we calculate the intersection of the building.
for (var building in buildingFootprints){
  var floors = IIF(building.FLOORCOUNT == 0, 1, building.FLOORCOUNT);
  totalArea += ( AreaGeodetic( Intersection(building, $feature), 'square-feet') * floors );
}
// Compute the ratio of the gross building area to the parcel area
Round( ( totalArea / AreaGeodetic($feature, 'square-feet') ), 1);