Decided to build myself a sluice a few years ago. After a bit of thought I decided to use plastic flute board from Bunnings. Worked quite well. It's so easy to work with, just measure, cut with scissors or a knife, fold it, hold it together with small nuts and bolts. Made it 6 ins wide, 90cm long (as long as the flute board). Then fold up a flare to feed the water in, attach that to the top. Didn't worry about riffles or anything fancy, just use a 6 inch dream mat with a bit of miners moss either side.