dear newtothis,
welcome to the muzzleloading fraternity, and welcome to those who are intimidated by the skill of some of the senior folks on this web.
some words of encouragement:
-- you're on the right site. there are a boatload of folks here who are knowledgeable, generous and supportive. there are a bunch of really good tutorials on this site as well. also, if you get stuck, the search feature will help.
-- if you've got the gumption to consider trying to build your own rifle, you probably have the stick- to- it necessary to see the product through. as it says in Deuteronomy, "be ye not afraid..."
-- although it isn't 'easy,' i believe that just about anyone with a modicum of patience and mechanical skill can build a rifle. there are some who would argue that they don't or can't do this, but i would posit that they need a boost of self confidence. their work might not rival the quality of some of the folks here, but it would be safe to shoot and be satisfying to know that this was their own work done with their own hands.
in my opinion, the coolest tools are the ones you make yourself.
by way of advice:
go for it!
more advice:
-- i agree with the notion of a precarve from Track of the Wolf or Pecatonica or Jim Chambers (depending on your budget). I started with a Tennessee kit from Track of the Wolf as a Christmas present for my wife. then i was hooked and there was no turning back. built some fancier rifles, but the mountain styles have always appealed to me. can't explain it, but the architecture of these guns is fascinating to me.
just checked the price at Track of their Tenn Mt rifle... wow- costs have crept up since i built mine!
-- get a few books on ML rifle building. if you can get a used one, my favorite is Peter Alexander's The Gunsmith of Grenville County, which i think is now out of print. When i bought my copy i thought it a great extravagance, but it more than saved me its purchase price in parts i didn't ruin and bad language i didn't use, as well as the odd blood stain on the wood. The Art of Building the Pennsylvania Longrifle is also a book you should own.
-- if you do decide on a kit from track, go with the .45 caliber. this is arguably the most versatile caliber available in a rifle (although i'm partial to the .40, but that's just me).
other comments:
the term "kit" might be misleading. this isn't like the model airplane kits you built as a kid, but will require a surprising amount of work on your part, since the parts won't fit exactly as you want them. there will be some inletting required, even with a pre- carved stock.
i assume that your grandfather has some sharpening stones and some chisels. if he has chisels and no stones, get the stones (or go the wet/dry sandpaper route - send me a private message for the details on this) if he has stones but no chisels, you'll need at least a few, but don't feel compelled to rush out and buy a bunch of sets of woodworking tools. often as not, you'll end up using only a few of the tools in the 'set,' and the others will just sit in the box and snicker at you for having cost you money while providing no benefit.
You'll want to get and keep your tools scary sharp. sharp enough to shave with is the bare minimum... get them sharper if you can. also, get some heavy leather and make a strop.
i discovered entirely by accident that there's no sin in getting the parts and then taking a long analytical look at what tools you will need to get them together. again: resist the temptation to go hog wild on tools.
oops! i almost forgot- there are some really good DVDs on American Pioneer Video. You can rent these for a modest sum, and the quality is pretty good, and the instruction is really excellent.
Best of luck with your first build- you're gonna have a great time!