Ideas for building wooden railway flatbed cars?

[Racer X]

MAVIC, Stone Way Hardware. They have a decent selection of magnets. And they are a small privately owned local store. I love that place. Second location is at the Ballard side of the Ballard Bridge. At the Ballard store, they are on aisle 15, halfway down on the left. At the Stone Way store, on the front wall. They might have wheel-like stuff. Further south on Stone Way on the west side, is Rockler. Great woodworking supply store.

Anyway, good luck. That kid has great parents!