// Before invoking this sample, select some walls to add a roof over.
// Make sure there is a level named "Roof" in the document.

// find the Roof level
FilteredElementCollector collector = new FilteredElementCollector(document);
collector.OfClass(typeof(Level));
var elements = from element in collector where element.Name == "Roof" select element;
Level level = elements.Cast<Level>().ElementAt<Level>(0);

collector = new FilteredElementCollector(document);
collector.OfClass(typeof(RoofType));
RoofType roofType = collector.FirstElement() as RoofType; 

// Get the handle of the application
Autodesk.Revit.ApplicationServices.Application application = document.Application;

// Define the footprint for the roof based on user selection
CurveArray footprint = application.Create.NewCurveArray();
UIDocument uidoc = new UIDocument(document);
ICollection<ElementId> selectedIds = uidoc.Selection.GetElementIds();
if (selectedIds.Count != 0)
{
    foreach (ElementId id in selectedIds)
    {
        Element element = document.GetElement(id);
        Wall wall = element as Wall;
        if (wall != null)
        {
            LocationCurve wallCurve = wall.Location as LocationCurve;
            footprint.Append(wallCurve.Curve);
            continue;
        }

        ModelCurve modelCurve = element as ModelCurve;
        if (modelCurve != null)
        {
            footprint.Append(modelCurve.GeometryCurve);
        }
    }

}
else
{
    throw new Exception("You should select a curve loop, or a wall loop, or loops combination \nof walls and curves to create a footprint roof.");
}

ModelCurveArray footPrintToModelCurveMapping = new ModelCurveArray();
FootPrintRoof footprintRoof = document.Create.NewFootPrintRoof(footprint, level, roofType, out footPrintToModelCurveMapping);
ModelCurveArrayIterator iterator = footPrintToModelCurveMapping.ForwardIterator();
iterator.Reset();
while (iterator.MoveNext())
{
    ModelCurve modelCurve = iterator.Current as ModelCurve;
    footprintRoof.set_DefinesSlope(modelCurve, true);
    footprintRoof.set_SlopeAngle(modelCurve, 0.5);
}

' Before invoking this sample, select some walls to add a roof over.
' Make sure there is a level named "Roof" in the document.


' find the Roof level
Dim collector As New FilteredElementCollector(document)
collector.OfClass(GetType(Level))
: Dim elements As System.Collections.Generic.IEnumerable(Of Autodesk.Revit.DB.Element)
elements = From element In collector _
 Where element.Name = "Roof" _
 Select element

Dim level As Level = elements.Cast(Of Level)().ElementAt(0)

collector = New FilteredElementCollector(document)
collector.OfClass(GetType(RoofType))
Dim roofType As RoofType = TryCast(collector.FirstElement(), RoofType)

' Get the handle of the application
Dim application As Autodesk.Revit.ApplicationServices.Application = document.Application

' Define the footprint for the roof based on user selection
Dim footprint As CurveArray = application.Create.NewCurveArray()
Dim uidoc As New UIDocument(document)
Dim selectedIds As ICollection(Of ElementId) = uidoc.Selection.GetElementIds()
If selectedIds.Count <> 0 Then
    For Each id As ElementId In selectedIds
        Dim element As Element = document.GetElement(id)
        Dim wall As Wall = TryCast(element, Wall)
        If wall IsNot Nothing Then
            Dim wallCurve As LocationCurve = TryCast(wall.Location, LocationCurve)
            footprint.Append(wallCurve.Curve)
            Continue For
        End If

        Dim modelCurve As ModelCurve = TryCast(element, ModelCurve)
        If modelCurve IsNot Nothing Then
            footprint.Append(modelCurve.GeometryCurve)
        End If

    Next
Else
    Throw New Exception("You should select a curve loop, or a wall loop, or loops combination " & vbLf & "of walls and curves to create a footprint roof.")
End If

Dim footPrintToModelCurveMapping As New ModelCurveArray()
Dim footprintRoof As FootPrintRoof = document.Create.NewFootPrintRoof(footprint, level, roofType, footPrintToModelCurveMapping)
Dim iterator As ModelCurveArrayIterator = footPrintToModelCurveMapping.ForwardIterator()
iterator.Reset()
While iterator.MoveNext()
    Dim modelCurve As ModelCurve = TryCast(iterator.Current, ModelCurve)
    footprintRoof.DefinesSlope(modelCurve) = True
    footprintRoof.SlopeAngle(modelCurve) = 0.5
End While