Got the first two flatcars knocked up outta styrene. Used scribe siding for the decks and cut timbers from .1 styrene. Woodgrain was distressed in with a razor saw. They ride on Tichy Train Trucks and use EZ Mate couplers.
I converted the last of the three flats I built into a high sided gon, also using styrene for the sides and tooth picks for the uprights. Stake pockets are sections of square styrene tubing and a section of styrene strip.