public new Multipoint ToGeometry()

{
  // Use a builderEx convenience method or use a builderEx constructor.

  List<MapPoint> list = new List<MapPoint>();
  list.Add(MapPointBuilderEx.CreateMapPoint(1.0, 1.0));
  list.Add(MapPointBuilderEx.CreateMapPoint(1.0, 2.0));
  list.Add(MapPointBuilderEx.CreateMapPoint(2.0, 2.0));
  list.Add(MapPointBuilderEx.CreateMapPoint(2.0, 1.0));

  // use the builderEx constructors which don't need to run on the MCT.
  // use AttributeFlags.NoAttributes since we have 2d points in the list
  MultipointBuilderEx builderEx = new MultipointBuilderEx(list, AttributeFlags.None);
  Multipoint multiPoint = builderEx.ToGeometry() as Multipoint;
  int ptCount = builderEx.PointCount;

  // builderEx convenience methods don't need to run on the MCT
  multiPoint = MultipointBuilderEx.CreateMultipoint(list);
  // multiPoint.HasZ, HasM, HasID will be false - the attributes are determined 
  //    based on the attribute state of the points in the list

  // or specifically set the state
  multiPoint = MultipointBuilderEx.CreateMultipoint(list, AttributeFlags.None);
  // multiPoint.HasM = false

  multiPoint = MultipointBuilderEx.CreateMultipoint(list, AttributeFlags.HasM);
  // multiPoint.HasM = true

  ptCount = multiPoint.PointCount;
}

{
  // assume a multiPoint has been built from 4 points
  // the modified multiPoint will have the first point removed and the last point moved

  // use the builderEx constructors which don't need to run on the MCT.
  MultipointBuilderEx builderEx = new MultipointBuilderEx(multipoint);
  // remove the first point
  builderEx.RemovePoint(0);
  // modify the coordinates of the last point
  var ptEx = builderEx.GetPoint(builderEx.PointCount - 1);
  builderEx.RemovePoint(builderEx.PointCount - 1);

  var newPtEx = MapPointBuilderEx.CreateMapPoint(ptEx.X + 1.0, ptEx.Y + 2.0);
  builderEx.AddPoint(newPtEx);
  Multipoint modifiedMultiPointEx = builderEx.ToGeometry() as Multipoint;
}