http://www.thecypressdepot.com/facts.html
This gives you a good example at calculating how much wood you'll need. With 10% waste added, you're looking at about 1,200 linear feet of 1"x6". 17'x28' shouldn't be too hard on the pocketbook. If you go the tongue and groove route, give them a call. You'd be suprise at how little the price difference between pine and cypress is. But once cry once!!