I've lost track of component/parts availability over the last three weeks (vacation)...but in the weeks prior, availability/pricing was still somewhat
problematic, despite the pricing and availability of complete ARs having nearly readjusted to-norms in the retail market (note: this applies only to both over-the-counter brick-and-mortar as well as via Internet sales; person-to-person sales in the secondary market still tended to be somewhat of a crapshoot as those who bought high during the panic are loath to reduce their asking prices to actual market norms as they're losing hundreds of dollars).
Before last December, yes, you could save significantly by truly piecing together your own.
Getting "exactly" what you want isn't necessarily that hard if you don't have a very, very specific set of requirements in-mind. This is especially true when it's so easy to simply "bolt on" aftermarket components. Gunsmithing? In reality, if you can work on your own car - change its engine oil, for example - you can very easily work on an AR, particularly if you invested a very modest sum in some specialized tools. This means that the change-out of most of the parts in order to more precisely fit your wants/likes can be easily accomplished. Usually, those who build their own to a list of precise parts are doing so to achieve end-goals that are beyond the usual wants of AR-newbies
or are really
looking at the absolute bottom-line (again, here, remember current market outlook - I would begin here by checking on M4Carbine.net's "The Official Where Can I Get It Thread" to see about the availability and pricing of the components that you'll need, as that thread is constantly refreshed/updated and will be market-true).
Yes, you'd get intimately familiar with the gun with a true
build, but the truth of the matter is that you can detail-strip a complete rifle and still get really, really familiar with the innards of the gun where it really mattered in terms of its functionality. On the flip side, while there are those who debate that it's more reassuring for newcomers to the genre to have the protection of a manufacturer warranty, the truth is that most component-build ARs will run just fine, as long as quality components are sought.
That is a great question but one that really does not have a single answer.
My suggestion is to price a few, fully built, AR's that meet your needs/wants. A few that are slightly below what you want but price out components to make it so. Then do some research in what it will cost to build a few similar rifles.
That will lead to your answer.
^ And that's the way I see it, too.
The only exception is:
As one that has never built an AR I can say that it really depends on what you want. Do you want just an AR or do you want something that looks like it is an alien weapon from another galaxy?
Given the current "tacticool" drive, this is no longer necessarily true. Building back-to-the-basics carbines/rifles is now also quite popular.