AreaReinforcement CreateAreaReinforcementInWall(Wall wall, Autodesk.Revit.DB.Document document)
{
    // Get the wall analytical profile whose curves will define the boundary of the the area reinforcement 
    AnalyticalModel analytical = wall.GetAnalyticalModel() as AnalyticalModel;
    if (null == analytical)
    {
        throw new Exception("Can't get AnalyticalModel from the selected wall");
    }

    IList<Curve> curves = analytical.GetCurves(AnalyticalCurveType.ActiveCurves);

    //define the Major Direction of AreaReinforcement,
    //we get direction of first Line on the Wall as the Major Direction
    Line firstLine = (Line)(curves[0]);
    XYZ majorDirection = new XYZ(
        firstLine.GetEndPoint(1).X - firstLine.GetEndPoint(0).X,
        firstLine.GetEndPoint(1).Y - firstLine.GetEndPoint(0).Y,
        firstLine.GetEndPoint(1).Z - firstLine.GetEndPoint(0).Z);

    // Obtain the default types
    ElementId defaultRebarBarTypeId = document.GetDefaultElementTypeId(ElementTypeGroup.RebarBarType);
    ElementId defaultAreaReinforcementTypeId = document.GetDefaultElementTypeId(ElementTypeGroup.AreaReinforcementType);
    ElementId defaultHookTypeId = ElementId.InvalidElementId;

    // Create the area reinforcement
    AreaReinforcement rein = AreaReinforcement.Create(document, wall, curves, majorDirection, defaultAreaReinforcementTypeId, defaultRebarBarTypeId, defaultHookTypeId);

    return rein;
}

Private Function CreateAreaReinforcementInWall(wall As Wall, document As Autodesk.Revit.DB.Document) As AreaReinforcement
    ' Get the wall analytical profile whose curves will define the boundary of the the area reinforcement 
    Dim analytical As AnalyticalModel = TryCast(wall.GetAnalyticalModel(), AnalyticalModel)
    If analytical Is Nothing Then
        Throw New Exception("Can't get AnalyticalModel from the selected wall")
    End If

    Dim curves As IList(Of Curve) = analytical.GetCurves(AnalyticalCurveType.ActiveCurves)

    'define the Major Direction of AreaReinforcement,
    'we get direction of first Line on the Wall as the Major Direction
    Dim firstLine As Line = DirectCast(curves(0), Line)
    Dim majorDirection As New XYZ(firstLine.GetEndPoint(1).X - firstLine.GetEndPoint(0).X, firstLine.GetEndPoint(1).Y - firstLine.GetEndPoint(0).Y, firstLine.GetEndPoint(1).Z - firstLine.GetEndPoint(0).Z)

    ' Obtain the default types
    Dim defaultRebarBarTypeId As ElementId = document.GetDefaultElementTypeId(ElementTypeGroup.RebarBarType)
    Dim defaultAreaReinforcementTypeId As ElementId = document.GetDefaultElementTypeId(ElementTypeGroup.AreaReinforcementType)
    Dim defaultHookTypeId As ElementId = ElementId.InvalidElementId

    ' Create the area reinforcement
    Dim rein As AreaReinforcement = AreaReinforcement.Create(document, wall, curves, majorDirection, defaultAreaReinforcementTypeId, defaultRebarBarTypeId, _
        defaultHookTypeId)

    Return rein
End Function