In N scale, shingles are a royal pain, particularly when you're modelling in cardstock. It's not just that you have to make hundreds and hundreds of tiny cuts, the problem is the white edges of those cuts are nearly impossible to darken with a marker or paintbrush.
Looking around the workspace, my eyes lit on a brown paper bag. PERFECT! I took my paper cutter and sliced one side of the bag down to 8.5" x 11", put it in the printer, and got a page of shingles that looks like wood through and through!
I've finished one side. When I got done, I used my tweezers to lift randomly chosen shingles here and there, hither and yon, higgledy-piggledy, to give the roof texture.
That clear plastic case, by the way, was thrown away by a vendor at an event where I was temping. It just happens to be the perfect size for this project. Score!