You can build on but it’s expensive. Some folks say AR-10s can be tricky to build. I decided to get a Seekins Coupon from someone on the Hide. The. I just bought a 6.5 SP-10 from Seekins Precision. Rifle shoots great. It had most everything I wanted anyway so it was a no brained for me. One other thing about it is that it is fully ambidextrous except the charging handle. You can flip the safety, lock/unlock bolt and mag from both sides.
https://www.seekinsprecision.com/product/modern-sporting-rifles/sp10-6-5-creedmore.html
www.seekinsprecision.com