Once you've selected your profile, carefully trace its shape onto a piece of particle board you've cut to fit it. It's very helpful at this stage to print the profile if you have a large enough printer or plotter available. You can spray-mount the profile to the first piece of particle board to make sure your cuts are precise. The two halves of the mold must have exactly the right tolerance between them, or the molds will not apply even pressure to your bent ply piece!
Once you've cut one carefully on the bandsaw, sand down using a (1" belt sander if available) to the exact edge of your profile curve.