structural calculations for home addition

I am looking for an experienced professional to provide structural calculations and design assistance for a home addition. The project is for a medium sized home addition of 200-500 sq ft. I have existing plans and blueprints and the main purpose of this addition is for a workshop/storage space. I am looking for an expert with knowledge of local codes and construction practices to help me make sure that my project is structurally sound and ready for construction. But mainly i need these calculations to obtain my building permit.