Entrance: A bedroom needs at least two methods of egress, so it should be accessible from the house (commonly through a door), and then have one other exit (window or door).
Ceiling Height: A bedroom ceiling needs to be at least 7 ft tall. It’s okay if some portions of the ceiling are below this level, but at least 50% of the ceiling needs to be a minimum of 7 ft in height. Most ceilings tend to be at least 8 ft tall, so ceiling height is not usually an issue (R305.1).
Escape: A bedroom must have one other method of egress beyond the entrance point. A door to the exterior works as an exit point, and so does a window. According to theInternational Residential Code, a bedroom window can be between 24 and 44 inches from the floor, it needs at least 5.7 square feet for the opening, and it must measure no less than 24 inches high and 20 inches wide (R310.1).
Size: The room should be at least 70 sq ft, and more specifically the room cannot be smaller than 7 feet in any horizontal direction (sorry, that 1’x70′ room won’t work) (R304.2 / R304.4).