What's the point, though? Statistically, most people who live deep in Tornado Alley will never even see a tornado in their lifetime. Getting hit by one is like winning the bad luck lottery; trying to build all buildings to be tornado proof would be wildly expensive and difficult to justify. Better to focus on good warning systems and making sure shelters are plentiful.

> will never even see a tornado in their lifetime

Could that be changing as the climate changes?

Like seeing 500-year floods several times in 20 years.

> A properly engineered reinforced concrete building would easily withstand that.

You could build a building like a tank, but it would price most people out of the market. Doors and windows in that structure won't be able to withstand the obscene wind forces however, so everyone inside will still likely be killed by the airborne debris, anyhow. You really wouldn't have time to install steel shutters on the windows and bar all the doors like you'd need to. But hey, the building will remain standing, so that's a win, right?

Instead of all of that, just requiring a small emergency shelter in each home might actually keep the occupants alive.