I keep this on file when someone asks about the "kits".
A little more on M/L building, there are a bunch of options available;
First would be what we call an "assembly" kit like a TC, Lyman, Traditions or CVA. The kits are mostly done and take very little fitting and work to put them together. Most of the work would be applying finish to the wood and metal.
A Kibler kits are next, very precise stock shaping, parts and stock inletting, some parts drop in, some have to be fitted with a little wood removal. Except for the lock and barrel all the other parts are castings and will have to be filed and finished. All of the holes are drilled in the stock but you do have to drill through the lugs and install pins. For someone who has done a CVA or tradition s kit, this would be a good next step. You will end up with a perfectly shaped historically correct rifle.
Since I wrote the above paragraph Kibler kits have evolved to have CNC shaped metal parts that don't need a lot of metal finishing before their use.
If you want an actual period rifle or fowler but doubt your skills you can buy a gun in the white, no finish on wood or metal but already assembled.
Third would be a parts kit with a precarved stock. These have all the parts but lots of fitting, drilling, final inletting ad some stock shaping is involved. Figure some wood and metal working skills and at least a hundred hours to complete this kit. The precarves I have bought have been flawed and took a bunch of work to correct the bad shaping errors. I have not put together a Chambers kit and only hear good stuff about them.
The best parts kits are available from Chambers, Track of the Wolf, Pecatonica and several other places with Chambers being the best.
http://www.flintlocks.com/ Here is a video on what is involved putting together a parts kit, lots of different videos covering each step.
Lastly is a scratch build I have made two of these, took me two years on the first, one year on the second and I suspect 6 months on the next. I kinda' know what I am doing now.