Pragmatically there are 20 main things to consider and 100 other factors.

Too many get tunnel vision on just the % and completely forget there is 3 factors to how the #'s wash-out; the rate, over what time, on what total amount.

The interest is added to the builder's cost sheet and factored in to the total cost to build. 

But there are other factors of a personal nature that will dictate when people want to use leverage or not.

As a private money lender, I'm curious to hear what makes an ideal lending relationship for you and how I can better support investors looking for flexible and fast funding solutions.

It appears you are focused solely on the financial components of the project without understanding the insurance and liability factors of self-performing the project in the manner in which you propose.

If you go into a different market and the laws change, you are stuck with a lease with someone who may not want to cancel it (not to say you couldn't have a clause in there).The main problem I have with this strategy is you are missing out some of the key wealth building factors that come with real estate.

From what I can tell, the most successful people who operate in C and even D class tend to vertically integrate their property management as most 3rd party managers just can't be compensated enough to make things work long term.

@Ashish Acharya Thank you so much for your feedback, I completely agree and have included seasonal trends and will look into economic factors including rental demand drivers.

I think that would play a big factor in how I would respond.