You can use Split Face on any non-family instance. The Split Face tool splits the selected face of the element; it does not change the structure of the element. After splitting the face, you can use the Paint tool to apply a different material to this section of face. See Applying a Material to the Face of an Element.
In the conceptual massing environment, a surface can host subregions that have their own properties. Creating subregions can help you refine your design and improve the accuracy of an energy analysis. You can assign a material to a subregion or extrude its profile into a solid or void form to change the topography of the surface.
To split a face
Projection type examples
Top down is useful for drawing skylights.
Parallel to level is useful for drawing windows.