I am a strong believer everyone should own atleast 1 or 2 rentals as a wealth builder for future. 

You need to account for Permitting Cost, Construction cost, Financing cost, Insurance costs (Builders risk & General liability), Holding costs, Selling costs, and contingencies for cost overruns.Any specific questions don't hesitate to reach out.

After scouring the market, I was able to get large builder financing and discount incentives that allowed me to buy the property at below retail price and get good financing terms.

If you know of a good area to look or any good builders in the area that would be great.

There's a misconception that builders are price gouging, but in reality, the price of a home is directly tied to the cost of building it.When material or financing costs go up, home prices follow.

We have a builder here in Utah that is building single family homes with fully separated basement ADUs.

You'll also have some builders that this may be the tipping point for them to not build new units in the area and go somewhere else.

If so, is that assuming that the builder builds at cost (and "proves" it by providing invoices/etc. by the subs)?

This becomes easer because the properties that we work with are new construction, so it is easy and fairly cheep to get the report done.We work with builders to help move their inventory of off market new contruction Investment properties at spacial investor prices and incentives.  

We are working with builders in great markets across Florida to get deal that work and cashflow day one for our investors.