10 and beyond with room rates starting at $399 a night and suites, $599. The company has begun taking reservations on its website and by phone for Dec. MGM National Harbor, the $1.4 billion, 308-room resort built by MGM Resorts International on the banks of the Potomac River in Maryland just outside Washington, D.C., will open its doors Dec. Subject to winning a gaming license from the state of Maryland, MGM Resorts International is proposing to build an $800 million destination resort in Prince George's County outside the nation's capital. In this artist's rendering, the proposed MGM National Harbor is seen from the adjoining highway that rings Washington DC.