What is a safe type of house for tornadoes?

Usually masonry walls fare better than wood and drywall construction. Avoid houses wild gabled roofs as those are more easily torn off. It is also good to see if it has anchor bolts to better secure the house to its foundation. Hurricane ties in the roof structure are also recommended, and can be installed later if your house doesn't already have them. New houses are usually better than old ones as houses tend to weaken with age.

Finally, and perhaps most importantly, make sure you can get underground either in a basement or a cellar on the property.