Better? What do you mean? Cost, Accuracy? I dont think it would be worth the extra cost to buy all the components for a complete upper build. Unless you are going to be building several uppers. When you go buying bolts,receivers, bolt carriers, tools, go no go gauges, barrels, hand guards, sights, etc. your not gonna be saving money. If you are wanting accuracy I would buy a complete match upper if you want it in the 5.56 caliber. If your wanting accuracy in a .308 platform I would build a custom bolt action on a remington 700 receiver, with picatinny rail, heavy barrel, HS precision stock, bager ordnance detatch mag.
Just my opinion, good luck