From Wikipedia:

Following the destruction of the original World Trade Center on September 11, 2001, there was much debate regarding the future of the World Trade Center site. Proposals for its reconstruction began almost immediately, and by 2003, the Lower Manhattan Development Corporation organized a competition to determine how to use the site. Public rejection of the first round of designs, the "Preliminary Design Concepts," led to a second, more open competition in December 2002, in which a design by Daniel Libeskind was selected. This went through many revisions, largely because of disagreements with developer Larry Silverstein, who held the lease to the World Trade Center site on September 11, 2001.

Source: https://en.wikipedia.org/wiki/One_World_Trade_Center

Also, check this:

• The original WTC was proposed in 1943

• Put on hold till 1949

• The site was made public in 1961

• Buildings weren't designed till 1964

• Construction started in 1966

• Ribbon cutting ceremony in 1973

Source: http://en.wikipedia.org/wiki/World_Trade_Center