Buy yourself a copy of "The Bowyers Bible" at least volume 1 and if you feel flush get all three. These will teach you a lot about wood types and charteristics as well as basic design. There is a good explanation of growth rings for the bow back and how to tiller properly. Read at least the first one and then find some wood. I would suggest that you start with something other than Osage for you first bow. Ash or hickory are very easy to work and much more forgiving for your first try. Make your first bow longer than you think you want, like 68 or even 70 inches long overall. It will be easier to tiller and you can always shorten it a little to gain a little more draw weight, because it will almost certainly end up at a lower weight than you hoped or expected after tillering.