Read up on all the factory guns with problems. While it's usually something simple that needs fixed, sometimes it's not.
It seems like the folks using budget parts (especially frames) or do 80% builds have the toughest time.
I built mine over time as needed starting with a factory gun that eventually needed a frame replacement. What remains from the original gun is the slide and a few small parts. Mine was lucky as everything fit with just a few file strokes and everything was dimensionally correct to start with. Many references were used as a guide but ultimately everything was fitted by trial, feel, and visual inspection. Back in the day any part purchased came with comprehensive instructions. These days they just come with a warning that it's a gunsmith fit component.
Along the way I broke a fancy sear spring, took too much off a thumb safety, and almost messed up a Colt frame installing an ambi mag release. It is not for the light hearted or inexperienced. A mistake on a slide, frame, or barrel is permanent and will cost some $$ to repair or replace.
If your time is cheap and you have the patience and skill go for it. As a first timer it is a daunting task. Literally everything but grips and some springs have to be fitted unless you do an all GI build. If I made a living of it I'd go broke in no time.
Most of the time working on mine had me sweating profusely, not for the effort involved, but in fear of destroying a $250 part
I love my gun as it is all mine and is reliable, smooth shooting and accurate. Unfortunately it is next to worthless as a home brew mixmaster only it's owner can truly love or appreciate.
It's pretty much the opposite of building an AR-15. Almost nothing is plug and play. "Drop in fit" almost never actually just drops in.
* I will add that doing it wrong, especially barrel fit/timing, sear/hammer interfaces and safeties can result in a dangerous gun and possibly one that destroys itself in short time.