The word "rooftopping" first appeared in a book called "Access All Areas" in 2005 by author Jeff Chapman. In this book Jeff refers to this activity as an offshoot of urban exploration. It's been called skywalking, roofing, and most recently New York Magazine called the people who do this "outlaw Instagrammers.”
Call it what you will, people have been going on roofs for decades (and probably even longer) for their own reasons, from Dan Goodwin's stunts to Philippe Petit's rope walk across the World Trade Center towers. Exploring rooftops is nothing new.