You have two choices, hire someone who is willing to teach you how to estimate (online or physical), or self-teach by buying some books like J Scott's book or Construction installation encyclopedia.

I earned a bachelor's degree in construction management, and currently work in that position for a production home builder.

We are thinking about buying and building out one to put temporarily on a property we are developing and rent it via Airbnb until we are ready to begin construction of the quadplex on that part of our land, and have it for sale during that period of time.  

Regardless of what I had I stayed in the construction business.  

Seller financing usually comes into play because of three situations1- Property is not financable (construction defect, hazard, uninsurable, needs extensive rehab, etc.)                                                  

I'm a WNC native with a family history in construction and insurance.

Disclaimer: I am not a professional electrician.Yes, you have to provide a GFCI outlet in a bathroom.For new construction, I think the bathroom has to be on its own 20 amp circuit, but I'm not sure that's always been the case; it may have been 15 amps in the past.Like @Donald Howaniecsaid, you can get a combination GFCI and switch that fits in the space of one "regular" switch or outlet. 

a proper builders risk policy is written to cover RCV or ACV if ACV is greater when construction is complete you need a standard dwelling policy.

Identify housing style, amenities and newest construction practices for today's buyer.*5.

Construction should last around 2 months.