I'm totally aware it's never going to happen in my lifetime, but theoretically, (for all you structural engineers out there), how much do you estimate it would cost to put a roof on the Horseshoe, or the Big House, or Penn State's "Erector Set" stadium?

What do you the time frame would be? All this talk about the 'Shoe or Big House hosting a CFP game and electing to host it in Indy or another indoor stadium made me wonder if it's even theoretically possible. I get that we'd be talking billions of dollars, but is it theoretically possible? I suppose you could argue to just build a second indoor stadium but since this is entirely academic, how awesome would it be to dome the 'Shoe.

It would easily be the largest indoor stadium in the world right? How awesome would that be? Or even if it had a retractable roof like AT&T stadium?