How did those guys get on top of that beam on the skyscraper?

They climbed up to the top of the building or got a lift on a crane... When you have to work at those heights you need to get over a fear of falling very quickly. In this day and age, it can't be done. Health and safety would have a field day, and consequently that's why it takes longer for buildings like this to be built, and also one reason why it's more expensive... Risk assessments are the norm now.