Having just built a pool using a local contractor, and having had a very positive experience (60 days, start to finish), I can tell you that the value add of a good contractor is in several areas:

(1) They know the subs, and get preferential responses to their calls. You are a one-time buyer, the subs don't need you nearly as much.

(2) The contractor, if they are good, will check the site before and afte each sub visit. They know what to look for. As a first time pool builder, you won't. IMHO, even reading this site won't prepare you to do it yourself.

(3) When one sub doesn't show up, things will snowball. See #1.

Key to this is finding a good pool contractor. Get references, and consider their size. My guy was recommended, and he does 30 pools a summer. There are contractors who do many times that. That made a difference to me, as I knew my contractor would personally see the site once a week (even if just for 10 minutes), and that his crew was small and (hopefully) reliable.

It worked out for me.