I've heard it too, as a matter of fact, a couple weeks ago on coast to coast there was a guest who discussed this theory. I enjoy entertaining the notions of stuff that is wayyy out there.

www.coasttocoastam.com/show/2015/05/21

In the latter half, professional game tester and proprietary software trainer Mark K. Sargent discussed his breakthrough work on the Enclosed Earth Theory. He outlined clues that point to the idea that Earth is actually a "Truman Show"-type contained system stretching thousands of miles wide, and 400 miles high. His interest in this theory developed out of studying "flat earth" conspiracies, which seemed absurd at first. One source, who said he used to work for NASA, claimed that the space agency knows that Earth isn't really shaped like a globe, Sargent reported.

Sargent's Enclosed World model differs from 'flat earth' theories in that he envisions a gigantic, but specific enclosure that stretches high enough to include weather systems. The moon and sun are not what we think they are-- they're actually much smaller spheres, like huge light bulbs, that are much closer to us than the distances NASA has suggested, according to the theory. Space missions such as to the moon and Mars could be faked, he added. Sargent also shared data from Admiral Byrd's expeditions to Antarctica-- he did numerous missions there over a 30-year period, and there's possible evidence to suggest he found something that correlates with or reveals the 'Enclosed World' secret.
Here's his website: http://enclosedworld.com/