How you make the tallest building

The One World Trade Center building isn't yet finished but the decision to declare it the tallest in America has been a bit controversial.

The title's changed hands plenty of times over the years, but since the 1990's it seems that being the tallest building is all about what you've got at the very top.

Ricky's been looking at the tallest buildings in America and around the world and finds out what it takes to be tall!