Local building codes, as well as state building codes will be available from your local (city or county) buildings and inspections office. If there is not a local office, you should check with the state building codes office.
Many cities, counties and states now make their building codes, specifications and other relevant information available online. You will also need to check on zoning laws and requirements in your city or county. In many communities, exterior changes and elevation/height changes will also require approval by a neighborhood or homeowners association committee.
If you own a historic home, you will may also be required to conform to specifications of the historical society or the historic preservation society.