Step 1: Materials
I like to get my oak boards in 3 inch widths, 5 to 8 foot long. I pick through the boards to find ones that have flat grain that runs straight for the whole length of the board. The longer the board, the less likely it is that its grain is going to be straight for the whole length of the board. The boards should also be free of any irregularities in the grain.
Ribs need to be about 8 inches longer than the width of the gunwales where they are being inserted. For estimation purposes figure an average of 24 inches per rib. Lets say you buy boards that are 5 feet long and 2-1/2 inches wide. Your ribs will be 1/4 inch thick, so you can get about 7 sticks out of each board assuming you lose 1/8 inch per cut. Each of those sticks will give you two ribs, so each board will give you 14 ribs. Allowing for breakage means that you will probably need three of those 5 foot boards to make all the ribs for your boat.