How can i turn my front garage into a bedroom?

I am thinking of renovating my front garage into another bedroom for when our twins are older they can have seperate rooms or a play room for our twins, It has already got a window, if i remove the roller door and replace it with a large window would that ventilate the room enough for somebody to be able to use it as a bedroom? i have already cleaned the garage out we have never used it for our car as we have another carport next to this one, has anyone got any ideas?