The scale ranges from F0 for the weaker storms to F5 for the catastrophic ones. As they spin on the ground, they move and are unstoppable. Anything coming in contact with them are usually done for. Trailer parks are the worst places to be in these situations, as the pressure builds up so much, the trailers just explode. Most of them only stay on the ground for a few minutes, while some have been known to stay on the ground for about an hour.
Some storms can be narrow while some some can be very wide.
A tornado that has mini-tornaodes spinning around it, sometimes even up to 5. While most spin counter-clockwise, every now and then a storm will be spotted spinning clockwise. These are very rare. If you want to know more about tornadoes, check out these other sights on tornadoes. There are also some pretty cool pictures of tornadoes on some of them as well.