Has anyone built a "swayback" structure ?

[Prairie Trains]

I use Campbell shingles on card stock on some of my roofs. When you apply them you have to use a couple of sheets of wax paper and a heavy flat weight to keep them from warping while they dry. If you let them warp a little it gives a sagged look. Its hard to see in these photos but it is easy to see on the layout. If you want a sagged ridge line you could trim the ridge line in a sleight curve to bring it down.