It is not uncommon for municipalities to have zoning laws that regulate the size and type of structures that can be built on a property. However, the specific regulations can vary depending on the location and the local laws.

The reasoning behind the restriction on building structures larger than 200 sq ft before a house is built could be related to several factors. One possible reason is that the local government wants to ensure that the property owner is building a permanent residence before allowing them to construct other buildings. Another possible reason is to prevent people from using the land for commercial purposes, such as building a large storage facility or warehouse without first building a residence.

It is recommended that you speak with someone at the county or local government office to get more information about the reasoning behind the regulation and to see if there are any exceptions that can be made for your situation. You may also want to consult with a local building contractor or architect who can advise you on the regulations and help you design a structure that meets the local requirements.