The first few years I built, I made a full size drawing of the rifle I intended to come out with on paper.
Any more, I just draw the profile on the side of the stock blank so I can saw it out on the band saw. Then everything else comes right out of my head..
I have an idea of what I want the gun to look like and order the parts before hand. However, haven't ordered any parts in a number of years, just working with stock on hand.
I generally have Dave Rase inlet my barrels for me.. I don't have any problem doing it, but Dave makes it easy.