It is all about the square footage.  1. 

For example, if the maximum attic height is 7' and the footage is 10'x10x, what's the effective square footage of the room? 

Generally, any property 4 units or fewer is going to be valued based on square footage, but there are diminishing returns the larger a house gets (with a few exceptions- notably, super high end properties).For example- there is a corporate mega builder in my market and they build out subdivisions of hundreds of homes at a time.

I work probably 60 hours a week and my wife is sometimes asking me why.Last week I was out in my open top fun car in beautiful fall weather shooting video footage of new subdivisions for my YouTube channel.

If my client is able to get the permit approved with certificate of occupancy, would the extra 400 sq ft (garage size) be applied to the total square footage of the house?

Thanks ManoloI'm thinking a total square footage of 800 square feet.

And yes, single family homes have already appreciated 100k+ since the announcement a couple years back, but if you can add value or square footage to a home you can still come out with a nice profit in the area or increase your cash flow if you are going the Air BnB route. 

Definition: A method of calculating a tenants utility usage based on occupancy, unit square footage, or a combination of both. 

Do they use a monitoring system such as noise aware/Minut, do they review ring doorbell footage on a typical Friday/Saturday night to make sure there are not 20+ people coming in for a party?

Dan depending on the area cost per sq footage is a good way to go.