Start with a 308 lower. There are 2 different types (I think) so decide which way he wants to go: AR10 or LR308. Once he has the stripped lower, then he can piece together the rest and build the gun how he wants.
It is far more important to be able to hit the target than it is to haggle over who makes a weapon or who pulls a trigger.
— Dwight D. Eisenhower