Build America's Libraries Act This bill establishes and provides funds through FY2023 for the Build America's Libraries Fund, from which the Institute of Museum and Library Services (IMLS) must allocate funding to states and, through them, need-based grants to libraries to make long-term improvements to library facilities. The IMLS must also award grants to Indian tribes and organizations that primarily serve and represent Native Hawaiians. Specifically, the bill requires each state that receives an allocation, and each library that receives a grant, to carry out certain activities to improve library facilities. These activities include constructing and renovating library facilities, investing in infrastructure projects to improve internet access and connectivity, improving indoor air quality, and making facilities accessible to individuals with disabilities. The bill also outlines administrative and oversight provisions, including by requiring library projects to use iron and steel products that are produced in the United States.