BCM is a great choice. Be sure to know what you want the AR for, then buy the upper that fits. I like 16" midlength with the pencil barrel. Think about the handguards/sights you'll want.
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together.
US Army 1966-69, VFW Life Member, Retired Geek