Doing an OB, it’s your pool and your project to manage. You select and hire subs as needed, you deal with municipal inspections, permits, spoils & trash, spec and select materials, finishes, equipment, schedule the work and supervise what you pay for. It’s a lot of work. On saving money, once you have selected subs, you can ask if they will work with you on price by offering to do some of the prep work. If you have the skills, then I would say explore the areas you feel confident in completing to save some cash. However, you will need time, Cash, tools and manpower at your disposal. I am an avid diy guy & work as a construction Manager for a GC. I have a decent skill in a variety of fields and both my neighbor and I have construction contacts, so it was pretty easy there. On the flip side, as an OB, you are competing with PBs for subs, so you will almost always take a back seat in terms of scheduling. Once spring hit, everyone got real busy so it added to the lead times. Just plan accordingly.
On the turndown, the designer spec’d cmu for raised beam & deck areas to reduce costs. Our engineer preferred concrete either with the pool or later with steel done initially. We did the math and while block was a little less, it added a build step to the process. We also considered the finish tile connecting to two different surfaces and the issues with expansion, cracking, etc... We opted to shoot the beam and raised walls with the shell and IMO that was the best as once shell was done, its one monolithic block of cement.
We are about wrapping 2 OBs up, both get plaster in a couple days. As a joint project, we did the all the back fill, grading, rough & finish electric, decks, pavers , flat work, finish gas work, and we will build the kitchens, fireplaces, etc... We paid Subs for excavation, steel, plumbing, shell, tile and plaster. I’m ahead about 30% overall of what my PB bids were, and we added some upgrades along the way. That said, it’s a lot of time and money to put in. If I paid myself I would be in the red by hundreds of hours of labor. But we knew that going in.