I've built wood cradles, but they get heavy when they have been used all day, I would recommend a build from aluminum sheet. Size is up to you. They are great for moving volume where water flow and availability are in short supply or the drop isn't adequate for a sluice box. I build mine about 2 feet long and the drop should be about 1 and 1/2 inches per foot. the apron baffle inside the hopper needs to be sloped at about 30 degrees, most of the gold should be caught on the baffle just under the classifier. Keep the riffles shorter, I like slightly more than a quarter inch straight up and down riffle, this is because they don't wash the same way a sluice does, gold will stop in the concentrates before the riffle not lay in an eddy behind it. This is because the water puddles in front of the riffle and creates a fluid bed or quick sand if you will. Rocking though not necessary keeps that fluid bed loose like panning does when the gold is moving, allowing it to sink into your concentrates and be stuck. If there are a lot of black sands they tend to fill the rocker quickly.
