Having known a couple of people who have done this, I can say that it's not terribly difficult. There can be some challenges with parts being at either extreme of the tolerances allowed for the individual parts, but I've only heard about one instance of that, and it was relatively easy to mitigate. There are instructions that walk you through the process of finishing the AR platform guns, and if you're mechanically inclined with some patience, I'm sure that you could get it done. I'm still saddened after having lost all my guns in a boating accident the last time I went fishing.
