Built a couple. If you go to the Track of the Wolf web site they include instructions for the production muzzleloaders that they sell. Very instructive and gives you a better idea what you are in for.
Would highly suggest that you avoid the "barrel, stock and bag of parts" route for your first one. The potential is there for a very nice rifle but are your skills up to it? Develope your skills and knowledge first and then try the "barrel, stock etc" route.
If you can find a copy of it there is a video by Hershel House where he builds a rifle from scratch. Well worth the time but keep in mind he has been accused of makeing what ever part he needs from the first piece of metal that comes to hand. He is that good.