The cross ribs are made from "five ply", half inch plywood. Getting a screw into four ply is just too time consuming. Ribs are one and a quarter inches wide and will split easily. External grade plywood is fine, as long as you fill any gaps you find, or, if a gap is really severe, cut a new piece. It takes less than half a sheet of plywood to build a boat, so the expense is not great. The longarongs are ash ripped to three quarter by five eights inches. The floor is made from a four inch, clear piece of white pine on most boats. On boats for my own use, I use a piece of ash one by one and a quarter inches. This works well, but unless you have infinite patience, don't try it. Keeping it straight while the rest of the boat is built up from it, can be very trying. These boats are very light, roughly 30 pounds, and not as fragile as they would seem at first glance. My friends joke that I will paddle on wet grass to get a good look at a turkey or an otter. Building time is about 80 hours, at an average work pace. The hull is #10 cotton duck, painted with an oil base paint. At times I have used synthetic rubber or hypalon, but I prefer working with the paint. The decks are covered with polyester backed vinyl that can be purchased in any dry goods store.