I would like to start a cleaning service for new construction houses in the Spring Hill, TN area. How much should I charge per square foot for a total interior cleaning, including windows? If more than one cleaning is needed before the new home owner moves in, how do I charge for each cleaning service after the first cleaning cost? Do I charge again per square foot or per hour?

You estimate and charge per hour, same as every other residential/commercial cleaning venture.

Everyone I know that does cleaning says never charge by the hour, charge by the job.

If you charge by the job, you are losing money. If the job goes into over time, that is where you lose it. If you charge by the hour, after estimating the square footage, you have a contingency.

I am charged by cleaners by the hour.

So how come you never mentioned this in my other answers regarding cleaning residential or commercial? You must have seen them, you answer almost everything here.

I guess I missed them.

One of the reasons I say you have to figure out all your expenses, and what all the job entails, etc... rather than hourly rate is because as you said it can take longer. When you do that type of cleaning you generally have to bid the total before getting the job.