I would take a piece of plywood, cut it desired length. I would take and put boards around the sides for the sides all around the wagon. I would then put wheels on the bottom of the wagon. The best thing I think you can make for the canopy is get you some small plastic pvc pipe and make some little brackets on the inside of the wagon so the pvc pipe can fit in it and stick it down in there to hold. The pvc will arch. Then put some cloth on the top or a tarp for the canopy.
