[iMagUdspEllr]

I built my AR from scratch. It was fine until I got to the upper receiver. You get to experience the "joy" of trying to get the gas block, gas tube, flash suppressor, and barrel nut lined up properly. You pretty much have to eyeball them and torque on them until you get them right. Or, you could just buy the parts and have those parts assembled by ADCO (like some wonderful members of this forum suggested to me).

The lower receiver is definitely doable yourself. But, if you don't line up the gas block correctly the rifle will be a single shot and/or it will be difficult to line up the gas tube.

If you don't line up the barrel nut correctly it also makes it harder to line up the gas tube

If you don't line up the gas tube correctly it will bind and cause failures when the gas key attempts to mate with the tube when the rifle cycles.

If you don't line up the flash suppressor/muzzle brake the muzzle device won't push the barrel straight down (but off to one side instead). You can get away with installing the muzzle device yourself because they don't interfere with the operation of the rifle and as long as you are fairly close you won't have a problem with it.

Its pretty easy to do it yourself. But, its pretty hard to get everything perfectly lined up. Maybe I'm missing something or I'm a noob or whatever, but its just easier and cheaper to have a company like ADCO do it.