Make a list of the functions you want your upstairs room to serve. For example, you may want to use the attic for storage and as a quiet homework and reading area, as a bedroom, or as a studio devoted to your craft hobby.
Have a building professional who is familiar with your area's building and safety codes examine your attic. Discuss your intended functions for the new upstairs room. Make a list or plan for what needs to be changed in order to make the attic comfortable, useful, and up to code. For example, you may need to enlarge one of the windows, add insulation and drywall, and refinish the floor.
Perform--or hire professionals to perform--the needed structural renovations, which may include electrical work and ventilation alterations. Make sure you obtain any necessary building licenses for the construction.
Bring in a government inspector or safety consultant to sign off on the new upstairs room as safe and up to code for its intended uses.
Finish the new upstairs room with paint, furniture, curtains, and other furnishings.