Additions, either to a dwelling or a garage, require a building permit. Construction plans should include a cross-section of the house, a floor plan, footing plans and a certificate of survey. See the addition/garage handout (PDF) for some code issues. Also, see the single-family lot guidelines (PDF) for standard setbacks from your property lines.
If a contractor is constructing the addition, the city requires the contractor to be licensed with either the state or the City of Maplewood. All gas work must be done by a contractor who is licensed for HVAC with the City of Maplewood.
Documentation required when applying for an addition building permit: