I've been pondering how to make textures of the Tuscany walls for weeks. Strangely this is the only thing of the entire scene that has been bothering me.
In the original Unity Demo the walls appear to be single custom bitmaps. I'm not sure if there is a better approach so I've asked for advice on the Substance forum.
This same approach applies to both the interior and exterior walls. I can certainly recreate them in Photoshop as a big texture and generate normals from that but maybe there is a better way through masks and layers. If I use a mask, the same mask will likely be applied to all channels
close up of texture