Get yourself a superior camera.
Buy a airline ticket to Washington D.C.
Take a taxi to the Smithsonian Institute
Walk to the basement gift shop.
As I understand it, the original 14 foot Enterprise shooting model from the 1960's is still on display there. If your intent is to construct a model featuring only the exterior of the ship, that would be your most accurate source of information.
If on the other hand you want to also have a complete interior to your creation, I'm sorry but there is no definitive layout to the entire interior of the TOS era Enterprise. The book The Making of Star Trek does have a (somewhat vague) description of what is supposed to be on various decks according to Roddenberry. And the Franz Joseph Booklet of Blue Prints while admittedly being a interpretation on his part aren't a bad place to start.
If you are going to proceed with this, please occasional post pictures of your work in progress, I for one would enjoy watching the build.