If you want complete control over the cost and type of materials you use, consider buying a tiny house plan. Some of the leading tiny house builders, who sell finished homes for $60,000 and more, sell the complete plans for those homes for $500 and less. If you don’t have construction experience, you’ll have a lot to learn as you go, but these plans are designed for DIYers. Some are available—from reputable builders—for as little as $79.
You should understand where the building will be parked or planted, ideally on a piece of land you own. Understanding where the fresh water will come from and where waste water will go is very important. Catching rainfall is a popular choice but not very reliable. As for budget, be sure you have a comfortable plan on how the project will be financed.