Although it is repeating what the others have said, there are basically two different kinds of "kits".
Lyman, Thompson Center and Traditions offer Kits that are basically semi finished production guns.
They don't require much except doing a little wood trimming, sanding and applying some type of wood finishing oils. Some of them will require bluing or browning the barrel and other steel parts.
With lots of sandpaper, a couple of screw drivers an Exacto knife and some little extras like a bar of soap and about 20-40 hours will get things done.
Then there is the Box of Parts "kits" that are sold by Pecatonica River, Track of the Wolf, TVM and others that consist of a semi finished stock, a unbreeched barrel, a semi finished lock and a bunch of raw sand castings which will eventually become the butt plate and trigger guard.
To build one of these "kits" you will have to have an electric drill, drill bits, taps, thread cutting oil, several files, a hammer, an Exacto Knife, several chisels, several screw drivers, lots of sandpaper, inletting transfer medium and several other things that slip my mind at the moment.
These "kits" will take a minimum of 130 hours for a first gun and may take as much as 200 hours to complete depending on how you want the gun to look.
The Factory kits can be modified but as the stocks are nearly finished there is not too much that can be changed.
Their big advantage is that most of the machining is done and the cost of the kit. Their big disadvantage is they will end up looking like a semi custom factory gun.
The Box of Parts kits disadvantage is the amount of work and knowledge needed to build them.
Their advantage is they will look like a fairly good to excellent reproduction of a 250 year old gun, depending on the skills and time that are spent in building it, that is made with excellent American made hardware.
I should also mention that there are a few places like TVM that will do all of the construction of the guns parts for you. These are total semi finished guns that will only require sanding and finishing the wood and browning or bluing the metal parts.
These cost a bit more than the "box of parts" and the choices of styles is more limited however they are good representations of the classic old style guns and they definitely do not look like a "Off the Shelf Factory gun".
On re-reading the first post in this topic mention was made of the Hawken style rifle.
If this description means a rifle like the rifle that Thompson Center produces, I would suggest Lymans Great Plains Rifle. It is an excellent choice but a bit heavier than the others offered by TC and Traditions or the Lyman TC copy.
If it means a "box of parts" version of a real Hawken it should be mentioned that this is one of the more difficult guns to build.