Supply can't keep up with demand, that's the problem right now. Hexcel and Toray are both building new carbon plants to try to reduce the shortage, which should stabilize things for a while.

The way I would make a hood: 4 layers of carbon, two on each side of a foam or honeycomb core, making a relief in the core thickness (if necessary) for the valve cover. If you want really stiff, a foam box frame around the outside edges (blended into the core) would really help, and make a convenient place to bond mounting inserts. The EG hoods I did were roughly similar to that, although more minimalist. If you want more impact resistance, another layer or two of carbon or fiberglass would be good, but won't really add much to the overall stiffness unless you add balanced layers to the bottom side also.