Building is easy,
True.
saves money,
You can save a couple hundred bucks. And if $$$ is a problem, you can spread the purchases out so it is less of an impact.
you get exactly what you want
Suppose you want a RRA Entry Tactical with an ACE stock and Vortex FH. Building it yourself saves the trouble and cost of having to replace stuff you don't want.
and you learn alot about the rifle.
Priceless.