There is a counter-point here. Typically the reason you hear from people looking to assemble their first AR is that they "get exactly what they want". On paper this sounds like a good idea, and they do typically get exactly what they want. The thing is that it's equally as often not what they need.
In some cases they at least get quality parts after a lot of internet research, but more often they fall into the "this part looks like that part" trap and have a hard time digging out of it. "I want a rail system" turns into a YHM, "I want a red dot sight" turns into a $100 chinese knockoff, etc.
But even with the good parts, if they don't leave enough money for magazines, ammo, and training they may be even worse off.
I know these things happen for two reasons. The first is that I see these people every month, twice a month, at our events. They have $2k in a gun they have no idea how to use, and often have some of their top-shelf parts installed incorrectly because they don't know WHY they want it, just that they want it. Or they have sub-standard parts that look just like what they thought they wanted and they can't figure out why the bullet fairy doesn't carry their projectiles out of the gun and magic them into the bullseye.
The second is that I did it myself. I tried at least to go about it in a reasoned way, and I researched all the parts, figured out what the top two most popular makes/models were, and bought them all. A Larue rail and a Daniel Defense, A Magpul stock and a Vltor, an Aimpoint and an Eotech, etc. and I assembled two guns with the parts, shot both, and cherry picked the parts and pieces from each that I liked best, then went and bought a Colt 6520 and combined all of the parts I liked best into that one gun. The thing was, I had no idea what to do with all those fancy parts, and only after going through all these machinations did I go and get some instruction on what to do with them. I would have been FAR better off, both in terms of becoming a better shooter AND in terms of my wallet, if I had simply bought that 6520 right from the beginning and gone and taken a basic class with it. The most expensive parts are the ones you try and get rid of at a loss because you don't like them (sometimes because you don't know how to use them correctly to begin with). So the idea that someone is "saving money" by "getting exactly what they want" is generally a fallacy as they don't know what they need and wind up changing things almost immediately once they start actually, you know, shooting.
But, for some the owning is all about exactly that, the owning. They like the erector set, gives them something to do in the garage that isn't quite as lame as building dioramas, and as soon as they are done "building" one they are on to the next one, with virtually no trigger time on the first, but that doesn't matter because the guns aren't bullet-launchers they are wall-hangers.