Extra Room / Library / House Extension?

I have a house. I have a lot of books and need an extra room / library. My back yard is big. My office room has a window to the back yard. Is it possible to put a door there and extend the house with an extra room? How much would a room cost, as big as a 2 or 3 car garage? What kind of company should I... show more I have a house. I have a lot of books and need an extra room / library. My back yard is big. My office room has a window to the back yard.

Is it possible to put a door there and extend the house with an extra room?

How much would a room cost, as big as a 2 or 3 car garage?

What kind of company should I search in the yellow pages?
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