Once you have your roof constructed, it is time to put some shingles on. The job looks harder than it actually is and gives a nice effect. To start, get some cereal boxes and lay them flat. With a ruler and pencil, measure out some strips between 1/2" and 3/4". Use a razor to cut them out, keeping the edges neat and smooth.
Some buildings had tin roofs as well. This is a much easier technique. Cut some strips about an inch thick and glue them evenly to the roof. Cover the seams with a narrow 1/8" strip and you are done! To paint, pick a metallic shade that you like and then wash it with some brown ink to weather it.
Keep in mind that spray paint will melt all exposed foam. Take your white glue and a paint brush and paint over all the exposed edges. Make sure all glue is dry before spray painting.
To begin painting, take your buildings out to the garage and hit them with some black spray paint. Don't bother using your $15 GW Chaos Black here. Go to the hardware store and find something for a buck. Even if you use ten cans you are still ahead! Put on a couple coats and make sure you get everything covered. Once dry take them inside, lay out some newspaper, and get painting.
I wanted some signage outside, so I downloaded some Wild West fonts an made up some signs on my computer. Having a color printer is useful. I printed them on tan cardstock and built a simple frame out of balsa wood, painted in the same fashion as the building. A little glue will stick it right on. I dressed up the porches with some barrels and other effects. You could put some static grass in the gaps on the boardwalk or glue some fines or bushes to the side of the building as well. More little details will add lots of realism.