Noel says that the inspiration for the title Who Built the Moon? was taken from a chapter in a book of conspiracies that he read in the 90s.
While I couldn't find anything with that specific chapter title, I think it's likely that Noel read Jim Marrs' Alien Agenda that was published in 1997 and became hugely popular.
The first chapter in that book addresses the Spaceship/Hollow Moon theory.
Guy Pratt mentions Who Built the Moon? by Christopher Knight and Alan Butler, but that book was published in 2005, so Noel may have seen or heard the title somewhere and gotten it mixed up. However, there are so many books on conspiracies it's entirely possible there is a book out there with a chapter titled Who Built the Moon?








