Curtain walls, curtain systems, and curtain roofs are host elements for CurtainGrid objects. A curtain wall can have only one CurtainGrid, while curtain systems and curtain roofs may contain one or more CurtainGrids. For an example of how to create a CurtainSystem, see the CurtainSystem sample application included with the Revit SDK. For an example of creating a curtain wall and populating it with grid lines, see the CurtainWallGrid sample application.