Sooo, is the question will it enhance the value, you need a contractor, or what steps will you need to go through?
If the question is will it enhance the value...maybe.
If the question is who could do this, I would go online for remodelers in the Phoenix area and thoroughly research each company.
If the question is what steps you will need to go through, first and foremost, you should have an architect and a structural engineer involved to determine if there is enough support with the existing framing to support the addition. For purposes of a permit for the improvement you will likely need a registered architect to draw the plans in addition to a report by a structural engineer confirming the design and the ability of the 1st floor to handle the weight. From there it is contractor time.
Feel free to give me a call, I have extensive construction experience as well as experience with the permitting process in Scottsale.