Hi Gemoke,
That would depend on the beginner. I have a Dunlap kit that I bought in June. I'm a beginner - I have built a couple pistols but that was 20 years ago and I kinda slapped them together at that. Since then, I bought a house and over the years, I've done my share of wood finishing and even built a cabinet or two. I've refinished a few modern rifles and shotguns, both wood work and metal work. But, I've never built a flintlock rifle.
The Dunlap kit requires final fit of the barrel, tang, lock, trigger, sideplate, nosecap, buttplate and ramrod ferrules into the wood. Metal parts have to be filed, sanded and polished. Wood has to be shaped and sanded, finished applied. Lot's of chisel, gouge and file work is involved. Holes have to be precisely located and drilled on wood and metal. Threads have to be tapped and dovetails have to be cut into the barrel. And that's without even thinking about carving and engraving.
Not saying a beginner can't do it - I'm trying to proove a beginner can - you'll have to judge if your beginner can do it. Some real experienced folks on this forum recommend a pistol kit or a GPR kit for beginners. Others recommend if you get one of these kits, get the trickier stuff done for you