public void SetHeight( 
   double height
)

//Modify an element's hieght.

//Perform on the worker thread
await QueuedTask.Run(() =>
{
  double elmHeight = element.GetHeight();
  elmHeight = 11;

  element.SetHeight(elmHeight); //You don't have to get to set; a shortcut would be: element.SetHieght(11);
});

//Create a north arrow for a specific map frame and assign a north arrow style item.

//Construct on the worker thread
await QueuedTask.Run(() =>
{
  //Reference a North Arrow in a style
  StyleProjectItem stylePrjItm = Project.Current.GetItems<StyleProjectItem>().FirstOrDefault(item => item.Name == "ArcGIS 2D");
  NorthArrowStyleItem naStyleItm = stylePrjItm.SearchNorthArrows("ArcGIS North 10")[0];

  //Build geometry
  Coordinate2D center = new Coordinate2D(7, 5.5);

  //Reference MF, create north arrow and add to layout 
  MapFrame mf = layout.FindElement("New Map Frame") as MapFrame;
  if (mf == null)
  {
    ArcGIS.Desktop.Framework.Dialogs.MessageBox.Show("Map frame not found", "WARNING");
    return;
  }
  //At 2.x -
  //NorthArrow arrowElm = LayoutElementFactory.Instance.CreateNorthArrow(layout, center, mf, naStyleItm);
  //arrowElm.SetName("New North Arrow");
  //arrowElm.SetHeight(1.75);
  //arrowElm.SetX(7);
  //arrowElm.SetY(6);

  var naInfo = new NorthArrowInfo()
  {
    MapFrameName = mf.Name,
    NorthArrowStyleItem = naStyleItm
  };

  var arrowElm = ElementFactory.Instance.CreateMapSurroundElement(
                            layout, center.ToMapPoint(), naInfo, "New North Arrow") as NorthArrow;
  arrowElm.SetHeight(1.75);
  arrowElm.SetX(7);
  arrowElm.SetY(6);
});

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

//Build geometry
Coordinate2D center = new Coordinate2D(7, 5.5);

//Reference a North Arrow in a style
StyleProjectItem stylePrjItm = Project.Current.GetItems<StyleProjectItem>()
                               .FirstOrDefault(item => item.Name == "ArcGIS 2D");
NorthArrowStyleItem naStyleItm = stylePrjItm.SearchNorthArrows(
                                       "ArcGIS North 10")[0];

//Reference MF, create north arrow and add to layout 
//var mf = container.FindElement("New Map Frame") as MapFrame;
var mf = layout.FindElement(MapFrameName) as MapFrame;
var narrow_info = new NorthArrowInfo()
{
  MapFrameName = mf.Name,
  NorthArrowStyleItem = naStyleItm
};
var arrowElm = (NorthArrow)ElementFactory.Instance.CreateMapSurroundElement(
  layout, center.ToMapPoint(), narrow_info) as NorthArrow;
arrowElm.SetName("New North Arrow");
arrowElm.SetHeight(1.75);
arrowElm.SetX(7);
arrowElm.SetY(6);