The first thing to realise when using consumer grade drives - even 'NAS grade' drives like the WD Red series - is that they fail. Often. And they fail without warning, without any chance of recovery. So if you want to keep your data, you have to plan on losing drives. For me, this means raid6 - for 4+ drives, any two can fail and still have all data recoverable from the remaining drives. It has slower read and write speeds than raid1 (mirroring), or raid10 (mirroring + striping, limited to 4 disks), but is also more flexible, as the pool can be expanded with additional drives.
Now, running raid isn't something one should set up through the BIOS - no consumer grade motherboard is going to include a hardware raid card, and that means it just runs software raid underneath the operating system, and still takes CPU resources. The problem, then, is that if the motherboard ever fails, you may have to find the exact model and revision to replace it with, as raid implementation quirks can differ between models, and sometimes even BIOS versions. Trust me, that's not something you want to deal with. So what do we do? Run software raid under Linux, of course! That way, the raid configuration is stored as part of the operating system, and is likely to be consistent across different machines. (Not to mention far more people work on and debug Linux's included raid utilities than the motherboard's)
So, get your favorite Linux flavor running, and set up a nice 12TB raid 6 array. Use any number of utilities to set up a SFTP server, and you're finished. And there you have it - a 12TB, redundant NAS for significantly less than any premade solution!