I'd like to politely disagree about the CIA Fals. I've got one as do both of my buddies and they are workhorses and none of us has had one moment of problems with them. The are also very accurate and I've shot my in competitions successfully. Ours were purchased in the last two years so are the latest "iteration" of the "unibrow" receiver and not the early versions which, in deed, has some problems with the Hesse receivers.
I embarked on a build myself a year ago Christmas in an attempt to build a second FAL. I must tell you that I'm experienced with tools. The problem I encountered with building the FAL was the locking shoulder and timing the barrel. With an L1A1, you need a breeching washer that will provide the proper timing. With a STG or "metric" FAL, there is another proceedure to follow. Both, however, require that you find the proper locking shoulder and that's a pain in the butt. Unless you have access to a handfull of different sized pieces, you'll go nuts trying to get that thing locking properly and every time you add pieces, you add money and shipping and handling thus increasing the cost rapidly. Add to that the cost of go/no-go gauges and special tools, and you're rapidly escalating your investment.
If,otoh, you purchase a CIA model, which will be an "inch" model, you'll have a shooter out of the box which you can then retrofit anything you'd like to create the model you want, as long as you stay in compliance with all the regulations in 922(r) [which is another consideration, btw. You can easily be out of compliance without the required pieces] . The unibrow receiver that CIA puts on their rifles has only been excellent to me and my friends and any lingering "issues" guys have had with the Century FALs have gone away.
So, spending about $450 for a working rifle and retrofitting on another $100 in new furniture or features is a lot quicker and cheaper than building from scratch.
Theoretically speaking, building a FAL won't take that long and isn't that hard if you have the special tools and a large assortment of bits and pieces at your disposal. And, building one is certainly a feeling of accomplishment. I've recently built an AR15 A1 and found it very satisfying. The FAL was a disappointment because everytime I turned around, it cost more and more and wasn't going to be worth it in the end. And this is regardless of which receiver you purchase, btw.
Just my 2cents. My best suggestion is to find someone locally who owns a CIA L1A1 and ask if you can try it. I'll bet you have a great time!
Rome