Until someone comes along and explains how to do this, which I don't,
I'll offer tip I use.
I make note of interesting painted walls, stone, etc. faced buildings or whatever and go back when I think the light is soft for that face.
Step back as far as you can (and try not to use a wide angle lens) and photograph as straight on as possible.
You want the largest face you can get, even if it has a window or door.
Clone out these and use generically. Eventually you will have your own library.
You can always crop down, but will have "tiling" if you have smaller image
than the object you are trying to cover.
Sorry if that's not much help.
Bier
