"In a way you get swallowed up by it, it's so big," he said. "Because it's such an incredibly big song that it doesn't need you to tell anybody, while you're eating lunch, [that] millions of people are going to be dancing on tables to that."
Mayer was around since the song's inception, and has watched the song evolve as Perry worked on it.
"I thought it was a really sweet, unforgettable sort of experience to hear someone's work while they still have a very nascent relationship with it," he said.
"Roar" leaked online last Saturday, prompting Perry to quickly release the song to radio later that day. A lyric video for the tune, off Perry's upcoming album Prism, was released on Monday.
Paradise Valley is streaming online now, and will be released on August 20th.