I painted the roof black then using computer printed guidelines & taped them to both side edges of the front roof section. I cut the shingles from 1/16" veneer at different widths - exposure 1/2" or 6" @ 1/12 scale. I let the shingles overhang the sides & bottom (eaves) 1/8" or 1-1/2" @ 1/12 scale.
I placed a piece of strip wood (with freezer paper glued to it to prevent the glue from sticking) at each increment of the guidelines & just placed some paint cans on the strip wood guide to hold it in position while I glued each shingle in place.
The roof was much easier to work with - as it was not attached to the dollhouse, but flat on my work surface. This is one of advantages of the modular design.