Custom AR-15 build

[The Gunners Mate]

Hi folks. I build custom AR's. I just picked up a CMMG 4SA (5.56/.223) rifle and plan to customize it. It has a standard butt stock, which I'm changing to a 6 point collapsable. The lower receiver is multi-caliber, 5.56,.223, 6.8, .300 AAC and .22LR. What do you think would be a great "build". Change caliber upper, hand guards, trigger pull, flat top or carry handle.......?

James
The Gunners Mate Shop