If you are planning on updating the structure of your greenhouse or demolishing a structure, you need to have a valid building permit before you can start the work. There will be an adjustment made to your tax assessment once a building permit copy has been forwarded to your local assessor. One of the most costly mistakes that you can make when building is not having a valid building permit, Depending on where you live, having an unpermitted greenhouse could mean you have to remove it or pay a large fine. Most building officials will help you with the process of getting a building permit. They want to make sure that your greenhouse or other building has been built to be safe for you, your customers, and your employees.