Typically, converting a carport to a living area violates many building codes and ordinances unless major changes are made. Carports usually have no foundation - they are essentially patios with roofs. The next best step for you, then - as the city said- is to hire an engineer to evaluate the structure, determine what's needed to bring it up to code, and take things from there. I would also address the home inspector. Presuming you had a home inspector involved in the transaction, this type of substandard construction should have come up during your the inspection. I would also talk with an attorney to determine whether you have cause of action against the home's prior owners, as well. The fact that a homeowner is able to sell a house doesn't mean they're not responsible for disclosing anything that's not to code.