that depends what you ranges you intend to use it for and what sights, iron sights, scope?. with iron sights. if you zero it at 36 yards. you will be dead on at 300 as well. scope. zero for what you intend to shoot most i would suppose.
If you want flexibility, zeroing at around 50 yards should give you the flattest trajectory, about +/- 2.5" from 0-225 yards. Otherwise zero at the distance you'll normally shoot.
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together. You'll remember the quality of a gun long after you forget how much you paid for it.
US Army 1966-69, VFW Life Member, Retired Geek