Well, for one, some new building materials and methods are unproven at best, and junk at worst.

Go off of what your contractors say, the book is broad and there is no way it can accurately estimate the cost of material and labor in every market with one number.

Where to promote?

Hey @Mandela Shaw - there are a couple of different resources available through BP as well, but what I recommend is going on Amazon and checking out the 'similar books' section since that's where you'll find relevant reading material as well. 

.- No matter where you're at, it seems like materials alone would cost more than $6500 for a roof and an AC. 

Usually the machine left for a couple days will really filter out the air and the materials in the house.3.

I use a written agreement that spells out exactly what they want to do, what materials they will use, when it will be finished, it must pass my inspection, if it is done improperly then the Tenant will pay for a professional to correct it, etc.

Research materials and their cost.

Join local Facebook groups and promote your listing there.

Just my 2 cents based on info we have Yes, I can get all 18-units done for $60,000 (labor and material for drywall, including mudding and sanding).