The "kits" from the main suppliers like TOTW, Pecatonica River, Muzzleloader Builders' Supply and similar companies consists of a roughed out stock with the general shape of the "school" with the barrel channel, the ramrod hole and the lock mortice roughed in.
All of the surfaces of the stock will require wood to be removed by filing, rasping or sanding.
The lock and set trigger will be finished but will need to have the necessary holes located, drilled and threaded for the fasteners.
Many barrels are not breeched so the breech plug will have to be installed.*
Many barrels will need to be drawfiled to remove the cutter marks from the exterior.
The sight dovetails in the barrel do not exist so they must be milled or cut in with a hack saw and a triangular file*.
The screw holes in the stock do not exist so they will have to be located and drilled in the wood.
All of the other metal parts are rough castings which will need to be filed, sanded and polished.
All of the parts like the trigger, the trigger guard, the butt plate*, the nose cap, the ramrod thimbles, the sights and the sideplate that goes on the opposite side from the lock will have to be inlet into the stocks wood.
The builder will have to finish the barrel channel, inlet the barrels breech plug tang, install the barrel underlugs* and drill the pin holes that will hold the stock onto the barrel.
The butt plate usually is not installed* so the stock will have to be cut and shaped to match the metal butt plate positioning it so that the length of pull is correct for the new owner.
The barrels vent hole (flintlock) or percussion drum will have to be located in the barrel, drilled and threaded for installation.
If a patchbox is desired (and almost all Kentucky longrifles had them) it will have to be located and inlet into the wood. The patchbox cavity will need to be created.
After installing all of the hardware the stock will need to be sanded and smoothed.
If it is Maple it should be stained and then oiled.
The metal parts like the barrel (and the trigger guard and buttplate if they are made from steel) will need to be browned, blued, polished or aged depending on what is wanted.
A regular kit from a major gun producer like Traditions, Lyman or Pedersoli will take the average guy 15-30 hours to finish.
The advanced "kits" from the suppliers will take anywhere from 120-180 hours of work to finish.
I don't want to scare anyone away from building one of the advanced kits but I think it is only fair to tell them about what they are getting into.
Another approach with these advanced guns is to look for suppliers who will supply the guns "in the white". That means they are assembled but the stock is not finish sanded, stained or oiled and the barrel is not browned.
After seeing what is required to build one of these rifles/fowlers it is understandable that the "in the white" guns will cost more than the box of parts does but they do save the newcomer the tasks of doing all of the necessary work.
* Things marked with an asterisk (*) are often offered by the suppliers for a fee.
Breeching the barrel and having the sight dovetails cut are two things I recommend for the first time builder.