I don't know how to build one, but Fred Bear killed an African Elephant with a hundred pound all bamboo bow, and a six foot arrow. So an all bamboo bow is not a fantasy. I have no idea if correct or not, but I would just get as thick a piece of Bamboo, and shape it to the shape you want, and then take succeeding pieces, and sand and shape and laminate them to the thickness you want, or laminate them, and then shape them, and then shape the bow in a form, then scrape the belly, and tiller it as you would a wood bow. And that is just purly guessing. I have absolutely no experience or practical knowledge in that area.
Good luck, and let us know how it turned out. Oh yeah, and lots of pictures.
Wayne