Mega-structures are products of engineering and construction on a massive scale. Often they require the need to overcome extreme obstacles and can take years to complete. We've put together a few modern structures which definitely fall into this category.
Sears Tower has been the tallest building in the United States since 1973. Construction commenced in August 1970 and the building reached its original maximum height on May 3, 1973. The tower has 108 stories and the distance to the roof is 1,451 feet (442 m) from the east entrance. Construction costs totalled approximately $150 million USD at the time, which would be equivalent to roughly $950 million USD in 2005.