Well (at least in the USA), there's nothing in the FARs differentiating between inside and outside when it comes to "in flight" and "for the purposes of flight". So if it's legal for you to fly it outside the barn, then it's legal for you to fly it inside the barn. Same goes for illegal, too - being inside a building doesn't eliminate the rules.
That brings up a side thought - those college students working on the human powered helicopter - none of them rated rotorcraft pilots, what's the call there?
