In this March 23, 2012, photo, an ironworker walks a steel beam at the top of One World Trade Center in New York. One World Trade Center, the giant monolith being built to replace the twin towers destroyed in the Sept. 11 attacks, will lay claim to the title of New York City's tallest skyscraper on Monday, April 30, as workers erect steel columns that will make its unfinished skeleton a little over 1,250 feet, just high enough to peak over the observation deck on the Empire State Building. The milestone is a preliminary one. The so-called "Freedom Tower," isn't expected to reach its full height for at least another year, at which point it is likely to be declared the tallest building in the U.S. (AP Photo/Mark Lennihan) In this Dec. 16, 2010, file photo, an ironworker connects a steel plate to a column at One World Trade Center in New York. The Empire State Building is visible in the rear upper left. One World Trade Center, the giant monolith being built to replace the twin towers destroyed in the Sept. 11 attacks, will lay claim to the title of New York City's tallest skyscraper on Monday, April 30, 2012, as workers erect steel columns that will make its unfinished skeleton a little over 1,250 feet, just high enough to peak over the observation deck on the Empire State Building. The milestone is a preliminary one. The so-called "Freedom Tower" isn't expected to reach its full height for at least another year, at which point it is likely to be declared the tallest building in the U.S. (AP Photo/Mark Lennihan, File) In this March 23, 2012 photo, an ironworker laughs at the end of his shift at the top of One World Trade Center in New York. One World Trade Center, the giant monolith being built to replace the twin towers destroyed in the Sept. 11 attacks, will lay claim to the title of New York City's tallest skyscraper on Monday, April 30, 2012, as workers erect steel columns that will make its unfinished skeleton a little over 1,250 feet, just high enough to peak over the observation deck on the Empire State Building. The milestone is a preliminary one. The so-called "Freedom Tower" isn't expected to reach its full height for at least another year, at which point it is likely to be declared the tallest building in the U.S. (AP Photo/Mark Lennihan) FILE- In this March 12, 2009, file photo, the Sears Tower, then the tallest building in America at 1,451 feet, rises above Chicago. One World Trade Center, the giant monolith being built to replace the twin towers destroyed in the Sept. 11 attacks, will lay claim to the title of New York City's tallest skyscraper on Monday, April 30, 2012, as workers erect steel columns that will make its unfinished skeleton a little over 1,250 feet, just high enough to peak over the observation deck on the Empire State Building. Workers are still adding floors to the so-called "Freedom Tower" and it isn't expected to reach its full height for at least another year, at which point it is likely to be declared the tallest building in the U.S. (AP Photo/Charles Rex Arbogast, File) In this March 26, 2012, file photo, One World Trade Center towers above the Lower Manhattan skyline and Hudson River in New York. One World Trade Center, the giant monolith being built to replace the twin towers destroyed in the Sept. 11 attacks, will lay claim to the title of New York City's tallest skyscraper on Monday, April 30 as workers erect steel columns that will make its unfinished skeleton a little over 1,250 feet, just high enough to peak over the observation deck on the Empire State Building. The milestone is a preliminary one. The so-called "Freedom Tower" isn't expected to reach its full height for at least another year, at which point it is likely to be declared the tallest building in the U.S. (AP Photo/Mark Lennihan, File) In this April 17, 2012, file photo, One World Trade Center, rises above the lower Manhattan skyline and the National September 11 Memorial, lower right, in New York. One World Trade Center, the giant monolith being built to replace the twin towers destroyed in the Sept. 11 attacks, will lay claim to the title of New York City's tallest skyscraper on Monday, April 30, as workers erect steel columns that will make its unfinished skeleton a little over 1,250 feet, just high enough to peak over the observation deck on the Empire State Building. The milestone is a preliminary one. The so-called "Freedom Tower" isn't expected to reach its full height for at least another year, at which point it is likely to be declared the tallest building in the U.S. (AP Photo/Mark Lennihan, File) This April 27, 2012, photo shows the Empire State Building, center, and One World Trade Center, rear right, in New York. One World Trade Center, the giant monolith being built to replace the twin towers destroyed in the Sept. 11 attacks, will lay claim to the title of New York City's tallest skyscraper on Monday, April 30, as workers erect steel columns that will make its unfinished skeleton a little over 1,250 feet, just high enough to peak over the observation deck on the Empire State Building. (AP Photo/Richard Drew) This Aug. 2, 2005 file photo shows Aon Corporation's worldwide headquarters in downtown Chicago. At 1,136 feet, it ranks as one of the tallest buildings in the country. One World Trade Center, the giant monolith being built to replace the twin towers destroyed in the Sept. 11 attacks will exceed the Aon Center's height and lay claim to the title of New York City's tallest skyscraper on Monday, April 30, 2012, as workers erect steel columns that will make its unfinished skeleton a little over 1,250 feet, just high enough to peak over the observation deck on the Empire State Building. (AP Photo/Charles Rex Arbogast, File) In this March 23, 2012, photo ironworkers connects steel beams at the top of One World Trade Center in New York. One World Trade Center, the giant monolith being built to replace the twin towers destroyed in the Sept. 11 attacks, will lay claim to the title of New York City's tallest skyscraper on Monday, April 30, as workers erect steel columns that will make its unfinished skeleton a little over 1,250 feet, just high enough to peak over the observation deck on the Empire State Building. The milestone is a preliminary one. The so-called "Freedom Tower," isn't expected to reach its full height for at least another year, at which point it is likely to be declared the tallest building in the U.S. (AP Photo/Mark Lennihan) This April 27, 2012, photo shows the Empire State Building, left, and One World Trade Center, right, in New York. One World Trade Center, the giant monolith being built to replace the twin towers destroyed in the Sept. 11 attacks, will lay claim to the title of New York City's tallest skyscraper on Monday, April 30, as workers erect steel columns that will make its unfinished skeleton a little over 1,250 feet, just high enough to peak over the observation deck on the Empire State Building. (AP Photo/Richard Drew) In this April 17, 2012, file photo, One World Trade Center, right, rises above the Manhattan skyline and the Empire State Building, center, in New York. One World Trade Center, the giant monolith being built to replace the twin towers destroyed in the Sept. 11 attacks, will lay claim to the title of New York City's tallest skyscraper on Monday, April 30 as workers erect steel columns that will make its unfinished skeleton a little over 1,250 feet, just high enough to peak over the observation deck on the Empire State Building, center. The milestone is a preliminary one. The so-called "Freedom Tower" isn't expected to reach its full height for at least another year, at which point it is likely to be declared the tallest building in the U.S. (AP Photo/Mark Lennihan, File) The sun reflects on a building as it rises Monday April 30, 2012, including One World Trade Center, center left, in New York as seen from Jersey City, N.J. One World Trade Center, the giant monolith being built to replace the twin towers destroyed in the Sept. 11 attacks, will lay claim to the title of New York City's tallest skyscraper on Monday. (AP Photo/Julio Cortez) New York's One World Trade Center is viewed from Jersey City, N.J., Monday, April 30, 2012. One World Trade Center will lay claim to the title of New York City's tallest skyscraper on Monday when workers will erect steel columns that will make its unfinished skeleton a little over 1,250 feet high.(AP Photo/Julio Cortez) In this March 23, 2012, photo, an ironworker walks a steel beam at the top of One World Trade Center in New York. One World Trade Center, the giant monolith being built to replace the twin towers destroyed in the Sept. 11 attacks, will lay claim to the title of New York City’s tallest skyscraper on Monday, April 30, as workers erect steel columns that will make its unfinished skeleton a little over 1,250 feet, just high enough to peak over the observation deck on the Empire State Building. The milestone is a preliminary one. The so-called “Freedom Tower,” isn’t expected to reach its full height for at least another year, at which point it is likely to be declared the tallest building in the U.S. (AP Photo/Mark Lennihan)