Wow, this is really looking good, especially the overlap zones with shadow. Is your roof model completely flat or do you have already modelled the steps? Did you do something special in the material definition? I would be very interested if you could share this material... Not fo re-use, but for understanding how it looks so nice.
I'm very flattered from your post: hearing that from a material pro like you is such a compliment to me!
..to tell the truth, my material is REALLY basic: just found a good base texture for the diffuse channel over CGtextures.com, and made it tileable with little PS work. Since each wood scale is lighter at the base (yellow-ish) and darker at the edge (grey/brown-ish) I tried to use that as a displacement map. The result was what I expected: fuzzy edges and insufficient ramping of the lines of tiles. So I manually added ramps in PS, going from white to black, to enhance the steps, as you called that.
Added some more precise subdivision settings to the flat planes of the roof and that did the trick.
All extremely simple. Material is a diffuse, too; nothing fancy.
I share the textures if anyone nedds those! (can I? If not, moderators can delete them and modify the post)