public CIMColor BlueRGB {get;}

//Must be on QueuedTask.Run(() => { ...

//Build geometry
List<Coordinate2D> plyCoords = new List<Coordinate2D>();
plyCoords.Add(new Coordinate2D(1, 7));
plyCoords.Add(new Coordinate2D(2, 7));
plyCoords.Add(new Coordinate2D(2, 6.7));
plyCoords.Add(new Coordinate2D(3, 6.7));
plyCoords.Add(new Coordinate2D(3, 6.1));
plyCoords.Add(new Coordinate2D(1, 6.1));
Polygon poly = PolygonBuilderEx.CreatePolygon(plyCoords);

//Set symbology, create and add element to layout
CIMStroke outline = SymbolFactory.Instance.ConstructStroke(
  ColorFactory.Instance.BlueRGB, 2.0, SimpleLineStyle.DashDotDot);
CIMPolygonSymbol polySym = SymbolFactory.Instance.ConstructPolygonSymbol(
  ColorFactory.Instance.RedRGB, SimpleFillStyle.ForwardDiagonal, outline);

ElementFactory.Instance.CreateGraphicElement(
  container, poly, polySym, "New Polygon", false);