Question about rolling pool into mortgage on new construction.

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My wife and I found a home we want to purchase in Mesa, Arizona. We are approved for a 1.2 million dollar loan. However, the house we want to purchase is only 611k. It is a new construction home that was completed two months ago. The front yard and backyard are not done, its dirt. I would like to landscape both front and back. Put in a backyard living room with kitchen with built in BBQ. Also, put in a nice pool. I am thinking about 150k of work. I do have cash to do it, but I want to preserve my liquidity. 

I want to know if I can roll this 150k backyard project into the mortgage? Is this possible? How do I do it? Is there anyone on here that does that sort of thing or has a reference?

Thanks everybody for your time!