The cost of building a 30×40 garage can vary depending on factors such as location, materials used, labor costs, and any additional features or customizations you may want. On average, the cost to build a basic 30×40 garage can range from $15,000 to $25,000. However, this is just an estimate, and it is recommended to get quotes from local contractors to get a more accurate idea of the total cost for your specific project.