There are 920 football fields of available office space in Manhattan. More than 180 major buildings totaling $12.5 billion in value — from Columbus Tower at 1775 Broadway to the office tower 400 Madison Avenue — are in trouble, meaning in many cases they face foreclosure or bankruptcy, or have had problems making mortgage payments. Rents for commercial office space fell faster over the past two years than in any such period in the last half century.