Tres bien...Nice Work!
First of all lets talk about the weak part in the actual VrayPattern... witch in my opinion, is the fact, that randomized texturing is almost impossible.
With your roof case, things are even worse!
I made a pattern for you, more or less as what you should make, in order to end up with a similar roof.
In fact, for making your pattern, you have to cut your tiles... this
makes the randomizing texture impossible...
for randomizing position and orientation, you have also no choice
with VP.
In many cases, using procedural textures in "world" mode can bring solutions, but not in this case.
You should also know that VrayPattern has no textures developed for, such as VrayScatter or MultiScatter textures.
Honestly, I would not recommend VP for doing such roof, because of the
huge importance of randomizing, required in texturing, positioning and orientations with your tiles.
Cordialement,
Djavadi