Lomcevak - I've never built up ribs, but I've seen it done. I wouldn't bother with it just to save weight because I don't think you will save any. I would do it for "artful" purposes or if I were using scale construction, but otherwise it's not worth the effort.

If you decide to do it, then build a jig that is the outline of the rib. Glue it to a base and then glue in jig pieces to align the bracing inside. Let's see... 30 ribs x 15 pieces each = lots of bracing to cut. Have fun!