A heavy dense wood like Cocobola or Ebony Ironwood makes good risers, bamboo makes for a good limb core. Bingham's has a great selection and if memory serves me correctly they can tell you the pluses and minus' of some of the woods. Also they have plans for all the things that go along with building recurves and long bows, from single piece to take downs.
Their number is 801-399-3470