Anyone know about building hard drives?

You can purchase two of the 3TB drives and put them in an external case.
You'll end up basically with the same as the pre-built solution in the second link.
But mind, you'll also need a good case. Seriously, a GOOD case, because the controller inside the case must be good in order to get good transfer rates.
Cheap cases have cheap controllers, and you don't want to use 6TB with crappy transfer rates.
So, with two drives and a case you won't be far from the price the complete solution provides.
Also, the 6TB thing has two drives in it, too, so if one dies you can replace the other.
Basically, with the 6TB drive you'll get what you want without having to build and setup it, for a not much higher price.

6TB is a monster ton of porn. Sure you need that much?

Cheers mate, will heed your advice.

NO, but for things like this:

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