The size of a structure that you can build without a permit in Texas depends on the zoning regulations of the area where the structure will be located. In general, if you want to build a structure that is more than 200 square feet in size, you will need to obtain a building permit from the local building department. However, there are some exceptions to this rule, such as for structures that are used for farming or ranching purposes.
In addition to the size of the structure, you will also need to consider other factors that may require a building permit, such as the type of structure you want to build (e.g., residential, commercial, industrial), the location of the structure (e.g., in a flood zone), and the intended use of the structure (e.g., as a dwelling, storage, workshop).
It's important to note that building without a permit can result in legal consequences, including fines and the requirement to dismantle the structure. Therefore, it's generally a good idea to obtain a building permit before starting any construction project, even if it's small.