Thirdly, I know his book was written few years ago, but his example has $2400 gross rent per month on a $100K property (which he bought for $80K). 

They’ll make at least six percent of the total fees, maybe more if they find the initial seller and the ultimate buyer.

Just my 2 cents.

Most of the experienced ones will be able to give you a ballpark per SF as a starting point, which may vary depending on price point and therefore level of finish out. 

In the past five years the average price of a home in Germantown has increased from $100k to $150k and the average rent per month has increased from $1,000 to $1,200.

I did also just Raise the annual rent  by $50 per month a separate and standard increse. 

The general plan is to try and get through 4-6 flips per year with (hopefully) a profit of around 20k each giving a projected profit of say 100k per year - (all talk at this stage). 

Now if it is raw land even with a ground lease the tenant wants to utilities stubbed to the site and the site ready to build on so you have some costs involved.In a ground lease you are getting ground rent so per the lease the tenant should be paying all the taxes,etc.

If you improve the property by investing, for example $20 per square foot, what would those improvements bring you in increased rents?

To take that even further they offer them per location.