The cost of adding a second story to a garage with 2x4 walls can vary significantly depending on various factors, including the size of the garage, the scope of the project, the region's labor and material costs, and the level of finishes you choose. Generally, adding a second story involves extensive structural work, including reinforcing the existing foundation and walls, adding a new floor system, installing new walls and roofing, and integrating utilities.
the average cost for such a project in the United States ranged from $100 to $200 per square foot. However, this is a rough estimate, and the actual cost could be higher or lower based on the factors mentioned above.
For a more accurate estimate, it is recommended to consult with licensed contractors or construction companies in your local area. They can assess your specific garage, understand your requirements, and provide you with a detailed quote tailored to your project. Always remember to obtain multiple quotes and thoroughly research the reputation and credentials of any contractor before hiring them for the job.