Call my contractor and neighbor, tell him the size, purpose, intended use of your addition. If it will be on a slab or foundation, tell him what your heating and cooling needs are. Tell him what style and type of construction the main house is.
Tell him how you want the addition to connect to the original house. How many square feet of windows, types of interior finishes to the addition. He'll have other questions too, I am sure.
Contractor, NRG Construction
916-677-7161 - Mobile
916-772-5675 - Home
Next answer to the question not asked.:
the added real estate resale value in todays real estate market, of the addition, will almost certainly be less than the total cost in todays dollars of building it.
Another answer to an unasked question: Never, never, never, ever never build an addition without proper building permits. It is the stupidest thing a person can do without matches. .