You cant do an upper or lower reciever in carbon fiber... well I guess you could but it would be $$$$ and it would only shoot once
+1the weight savings in the upper dont seem to be worth it considering the only carbon part being the stripped upper reciever. the stripped upper reciever only weighs a few ounces. if he wants light weight and affordable tell him to get a complete plumcrazy lower from u.s. arms for 130 and build the upper out of something like a 14.5 inch lw barrel with pinned flash hider. some light weight handguards (magpul moe, car) that way he can choose his barrel, his fsb, and just get a good bcg and hes set.