In the .308 AR product space, you have to choose which horse to ride, and then ride it.
The two choices you have are:
1. Armalite's AR-10. You need to buy uppers and parts kits that are compatible with the AR-10 lower receiver. There's very few suppliers of parts besides Armalite for AR-10 lowers/uppers.
2. DPMS LR-308. There's lots more suppliers of lowers/uppers that are compatible with the LR-308 dimensions.
So start by making that choice, tell us, then we can go from there.