Better Utilization of Investments Leading to Development Act of 2018 or the BUILD Act of 2018 This bill establishes the United States International Development Finance Corporation to facilitate the participation of private sector capital and skills in the economic development of countries with low- or lower-middle-income economies and countries transitioning from nonmarket to market economies in order to complement U.S. assistance and foreign policy objectives. The corporation may: (1) make loans or loan guarantees, (2) as a minority investor acquire equity or financial interests in entities, (3) provide insurance or reinsurance to private sector entities and qualifying sovereign entities, (4) provide technical assistance, (5) administer special projects, (6) establish enterprise funds, (7) issue obligations, and (8) charge service fees. The corporation shall terminate on September 30, 2038. The corporation shall not provide assistance to: (1) a country whose government has repeatedly supported acts of international terrorism, or (2) a private sector entity that is engaged in monopolistic practices. The bill prescribes transitional provisions, including transferring to the corporation the functions, personnel, assets, and liabilities of the Overseas Private Investment Corporation (which is subsequently terminated) and specified elements of the U.S. Agency for International Development.