Some random thoughts on designing tornado-resistant structures.

It's too expensive to make an entire structure able to withstand the wind loads of a 200+ mph tornado (or a hurricane).  Just adding in impact-resistant laminated glass, would price out most people, I suspect.  Then you have to double your structural members and anchorage.

Underground shelters / basements are not really that cheap and in some cases, not possible, given the type of soil present in much of the Midwest -- the land is nearly as flat as a Cartesian plane with rich soils, and there's a reason for that.

The pressure differential between the interior and exterior of buildings, creates lift.  You could design for extreme loads and incorporating venting mechanisms to try to narrow the difference in pressure, but that's expensive and an improbable task to retrofit existing homes and structures that make use of 2x4 wood studs at 24 inches on center.

A feasible and simple option, in my mind, is to incorporate those steel storage transport containers bolted down to a slab on grade concrete foundation.  You might see container trucks lifted into the air occasionally, but more common is to see them tipped to their side.  With a bolted down connection to a concrete slab, you don't have those problems.

You can retrofit existing classrooms or incorporate them into new construction, as an emergency shelter -- nothing fancy, but something to get you through, at a minimum, 15 minutes of hell.  There are some additional things that need to be added to them before they can be functional, such as battery-pack lights, indirect ventilation, an emergency beacon, a modified latch that can be operated from the inside, and of course appropriate sound insulation with gypsum wall board and carpeted floor.

If you want to get fancy, you could pop in laminated windows, and, if attached to a home, could function as a temporary residence while you rebuilt the rest of your home.