The flat roof of the dormer is finished in a faux-asphalt, achieved by base coating the roof with a thick layer of very dark, almost-black grey paint (I had leftovers from a quart bought for another project—use what you have, of course, but the paint does have to be on the roof fairly thickly), and then sprinkling a heavy, even dusting of black craft sand over the paint and gently (and very flat-ly), pressing the sand into the paint. Don't press so hard that you make the paint drip off the flat roof's edges! The paint becomes the base color and the adhesive. Be very patient, this takes a long time to dry.
When dry, shake off the excess/ non-adhered sand (I put mine back into the container I keep it in, to reuse at another time), and you should have a very realistic asphalt look.