The Boeing Everett factory in Washington, USA is not only the largest factory building in the world it also holds the distinction of the largest building of any kind in the world by volume. At a staggering 0.472 billion cubic foot this colossal building, occupying an area of almost 100 acres (0.4 million sq.m.) is second to none. This factory, which has been producing a slew of Boeing 747s, 767s, 777s etc., is also the production hub of the latest 787s, ie the dreamliners.
However, when it comes to floor area, Abraj Al-Bait Towers in Mecca, Saudi Arabia steals the show. The 600m tall 120 storeyed building boasts of a total floor area of about 1.5 million sq. m. It is also currently the 2nd tallest building in the world, the tallest being the Burj Dubai.
But, if the proposed Crystal Island complex in Moscow materialises, it would smash the largest floor area record hands down with almost double the floor area of the current numero uno. Crystal Islands is expected to host 900 apartments, 3000 hotel rooms, u/g parking facility for 16000 plus cars besides many other facilities.