you need to get a parts kit in good condition. it will not include the (BATF controlled) upper receiver.
you may have no more than 10 of 20 BATF specified imported components (17 applicable to FAL) when assembling so you will need an additional 7 US made parts if you want a threaded muzzle or 6 if you go unthreaded.
the building is not difficult. it's stopping that's the challenge!
the cliff notes:
first thing is installing the barrel (which threads) into the receiver so that your front sight sits at TDC in relation to the receiver while tightened within an acceptable range of torque.
once that's done, you use the kit's bolt & carrier to determine what size locking shoulder is needed to provide the desired headspace, you get that LS, bang her in and then it's just assembly.
provided all parts are in spec and good condition, you shouldn't have much trouble except feeding it and financing the next builds.
the tools can be improvised on the cheap or you can easily spend a couple $100. either way you go you'll probably need a vise. a receiver wrench w/breaker bar, barrel vise, go / no-go gauges and pin gauges (to help determine locking shoulder size) and barrel timing rods or some other means of indexing the barrel would constitute a good build kit. common FAL tools such as an extractor disassembly tool and buttstock removal tool should be in your toolbox if you're buying or building, either improvised or purchased.
i've read low cost methods using rather than all that stuff an open end wrench filed to fit the flats of the barrel, wood blocks to clamp the receiver in the vise, empty cases & masking tape for headspacing, etc but i went with purchased tools and am currently in the process of reducing my per-build tool cost by building #s 5&6
here are 2 links i referred to a great deal before / when i got started
BANDIT'S (use the links on the left)
CRUFFLERgo to
FALFiles Gunsmithing & Build It Yourself forum for anything else.
the parts:
(1) Frames, receivers, receiver castings, forgings or stampings
(2) Barrels
(3) Barrel extensions
(4) Mounting blocks (trunions)
(5) Muzzle attachments
(6) Bolts
(7) Bolt carriers
(8) Operating rods
(9) Gas pistons
(10) Trigger housings
(11) Triggers
(12) Hammers
(13) Sears
(14) Disconnectors
(15) Buttstocks
(16) Pistol grips
(17) Forearms, handguards
(18) Magazine bodies
(19) Followers
(20) Floorplates