One of the most important documents occurring in the investment process is the administrative decision: building permit. Obtaining it is often a time-consuming process in practice, associated with the need to attach to the application other required decisions and permits necessary for a positive consideration of the case. The procedure itself is not always a long-term process, as long as the investor makes sure to prepare a reliable application free of errors and irregularities together with the construction project and the required attachments. The purpose of the article is to analyze errors appearing in investors’ applications and attached project documentation required in the administrative procedure for obtaining a building permit in the light of the applicable provisions of Polish law.