I don't imagine it would be any harder than a typical AK. Those are not as easy as building an AR, but they're not impossibly hard either. It's hard enough to be considered real gunsmithing. You're going to have to find or make a receiver for it. That's going to be the hard part. If it doesn't come with a barrel, you are going to have to find one of those too, and head space it along with a few other things. I believe you'll also have have to make sure there are enough American made parts in it to make it 922r compliant
What is your experience with fabrication or using tools in general? Like I said, this is not an "easy" project in that you can just slap a bunch of parts together. You will have to know what you're doing and the right way to do it.
Are you doing this to save money, or just because you want to build an RPK? You are probably not going to save much money if any doing this, but there is something to be said of building a functional gun out of a bag of parts that makes it worth wild for some people.
I'm not trying to discourage you from doing this, just letting you know the reality of what you're wanting to do so that you don't go into it blind.
I would look up some of the tutorials people have done on building an AK. The RPK will be very similar, and it will give you a good idea of what it takes to build one.
Well, I personally own a semi-automatic RPK, so it can't be too difficult. As stated above, parts might be a bit tricky, and I don't think you're gonna save much money on it. I sure think it's a pretty neat addition to a collection though.