We "kind of" GC'd our own.
We hired a guy to design, engineer, and permit for us and he gave us itemized quotes for each step. He also gave us over all advice. We also got a friend of a friend to spec out our equipment for us as a favor and have it quoted from his supply house at his cost. We went through the equipment list and cherry picked big ticket items we could get cheaper buying on-line from discounters.
We ended up using the layout/dig/steel quote from the designer as well as his gunite guy. We hired a friend to do our coping/tile/pavers and used other references to find subs for plumbing, electric, screen and plaster. We already had guys for general masonry (screen footer) and landscape. We got the guy who built our waterfall as a reference from the yard that sold us the stone.
Over all we ended up about 10% below the best turnkey quote and had more features than the most expensive turnkey proposal. Our build was not fast, but it got done. We had two issues that caused a bit of stress and where I found myself wondering if having a PB would have been better. First... the automation setup was more difficult than I expected and for a while I was thinking it was not going to work - eventually I figured it out. And.... the pool had a leak

that took me quite a while to locate - but once I found it the fix was easy.
The bidding, scheduling, and coordination was a job that my wife spent a lot of effort doing. For sure a key for us was personally knowing a few people in construction and one specifically in pool renovation to give us references. All our subs were wonderful except for one who ended up being difficult and probably more expensive then he should have been (electrician).
We'd do it again - full story and pics here
new-build-in-lake-nona-fl-t54611.html