Well, shoot. I don't actually know what FDR would have done. Certainly not what Bush is doing.
But here are some things I do know:
In previous eras during national disasters, the National Guard and the disaster agencies would find room anywhere they could set up for people. Tents. Military bases. Whatever was available.
Within three hundred miles of New Orleans - about the distance to Houston - there are a fair number of military bases with permanent barracks that have few or no troops, given their deployment in Iraq. Some of those barracks may still be WWII barracks, in need of some work, but they beat concrete bleachers in a partially roofless, waterless, foodless, Superdome. The bases have what's needed to house tens of thousands of people, cook for them, provide beds, showers, bathrooms, and security.
Even military tents are preferable to rooftops and concrete. And I suspect they've got some of those lying around, too.
You have to wonder what the Bushies are thinking, if anything. They are blowing it so badly they will not recover.