I watched all the horrible news about the loss of life, the injuries, and the destruction of entire towns. Those who have suffered loss will be in my prayers.
Here, if I were building a new home, I would include what they call here a "safe room". Typically, it's an above ground room with an optimal size of less than 12' x 12'. Strength is diminished with larger rooms. Typical construction is thicker concrete heavily reinforced with steel. The room has an extremely heavy steel door, and the typical cost is between $2,000 to $3,000 extra. These safe rooms can double as a wash room, a pantry, or other uses that would utilize the area daily. If I understand correctly, there are tax advantages of building either a safe room or storm shelter that are significant.
If my wife and I ever build our dream home, it will be much smaller than the one we have now, and it will definitely include a safe room.