Maybe it's easy to forget, but the AR parts market is absolutely impossible to navigate as a complete beginner.
I must be some kind of wizard then because I did exactly this, while in the exact same situation as this guys friend.
It's difficult to do even as someone a bit more experienced in the ins-and-outs of the platform.
I just don't get why some people make this out to be rocket science when it really is a simple thing to do. I literally went from shooting a friends AR one day for the first time ever (30 rounds) to building one from stripped receivers without a lick of help outside of google. If this is difficult for someone experienced with the platform then I'd probably not want to be on the same firing line as them.
Sure, I see merrit in building, but I can't comprehend how people look at someone who is a complete beginner to the firearms world and just want to toss them straight into the deep end.
It's really more like a wading pool. Again, I was a total and complete newb when I built my first rifle, had
zero idea what I was doing when I first started. Didn't know a gas block from a bolt, or a buffer tube from a forward assist. Even further I had only been introduced to firearms a year or so earlier when I bought my first gun (XDM 9mm).
The way I see it, unless someone with a great deal of experience is helping find parts it's more likely to end up in a poorly performing rifle than had one ordered a factory complete rifle. Not to mention that if something does go wrong, there's no factory to send the complete rifle back to, as such it takes significantly more diagnostic ability to in order to make the rifle functional.
Like I said above, outside of google I had zero help figuring out what parts to buy and how to assemble it. On top of that I didn't even know what the parts were and what they did. However, there is so much knowledge available with a few short keystrokes. If you can use google and youtube there's absolutely no reason someone like myself can't research the AR-15 platform, figure out what makes them tick, put together a parts list, and then go figure out who makes good parts. Once you've done all that thoroughly, assembly is easy. Also once you've done all that
thoroughly, diagnosing and troubleshooting should be easy, especially using our friend google again and forums such as these. If someone can't use google to do so I'm not sure they should be getting into the AR world to begin with. The way I see it, any person wanting to build an AR needs to understand that it will take some time and research on their end to fully understand what they are doing, but it is certainly and easily doable by your average Joe.
The building itself is easy, as long as one follows directions, but pretending it's a simple as Lego's because of the ease of mechanical assembly is disingenuous. It's the guy's first rifle, if he can afford to buy one complete from a quality manufacturer he probably should. I doubt he'll notice enough marginal improvment on an AR built from QUALITY parts to make the difference in effort and risk worth it.
For me building wasn't about a noticeable improvement, in fact I'd wager most AR's of equal value whether built or bought off a shelf will function nearly identically. I also don't see how there's a greater risk with building if you can follow directions. Either way a human being is still assembling a factory rifle and we're all capable of making mistakes. I would agree though if the buyer can afford a quality factory rifle there's certainly no harm in buying it, I obviously just like the extra knowledge and satisfaction you get knowing you built it yourself ... that and building it the way you want it means you probably won't have to spend extra money down the road swapping out that factory grip / stock / handguard / brake / <insert part here> because you end up not liking the factory parts.
Also, long heavy barrels and match triggers? Defensive purposes were mentioned very very very early in the OP.
Long heavy barrel? Certainly not! Don't see any reason a quality trigger on any AR would be a bad idea though.
Sorry, that got really long winded, and I'm not trying to argue with you. It's just that someday someone is going to be on step 1 of wanting to build an AR and open google like I mentioned above and read this thread, and I don't want them scared off because someone thinks it's above other peoples skill level to build their first rifle from scratch!!