Living in Middle Tennessee where tornados are a threat with almost every storm, we plan on putting in an underground shelter in the garage like this:

http://www.safestormshelterstn.com/

A plywood reinforced closet doubling as a storm shelter is a joke, IMO. If you've ever been in the vicinity of a direct hit from an EF-4 or 5 and seen first hand the debris and destruction you'd know just how futile that entire concept is. To survive a direct hit from a 4 or 5 you need to be underground.

Here is a link that might be useful: Storm Shelter

There are several manufacturers if you Google. One like Parsonse linked goes under the garage. Only downside, your vehicle goes outside and could get damaged - nothing compared to saving your life, but when you come up and see a hailstorm or fallen tree has dented...

There is one that actually is built as a walk-in closet. Perfect for a new build (but can also be done in an existing home). The walls around the storm shelter/vault do not touch the shelter. Has a door that will secure. Otherwise, it looks like a normal walk-in closet. Won't have to move a vehicle to get inside, which is a plus. Quick access is sometimes of utmost importance.

In our house in Oklahoma, which I designed, we had a large reinforced concrete "closet" about 8' X 10' or 12', if I remember correctly.

The house had a concrete slab, from which we poured four reinforced 8" concrete walls, and a concrete slab for the top. A solid core door provided access. One could have used concrete block for the walls, but I wanted a stronger, monlithic poured wall. Switched lights and electrical outlets were included, but in case of loss of power we maintained flashlights and a battery-powered radio. We also had a camping lantern and stove there, in case needed outside the closet.

Regular, framed stud walls enclosed the concrete closet, so that from the hallway, one had no idea what was behind the door. We used it a couple of times each year, and kept folding cots and supplies inside. It was quiet, always stayed a consistent cool temperature, and was a good place to sleep during summer storms.

Good luck on your build.

We are putting in a cold storage room, for my wine and beer in the basment as a bonus it will serve as a storm shelter,

"We are putting in a cold storage room, for my wine and beer in the basment as a bonus it will serve as a storm shelter,"

Nice for you, but the OP specifically said that a basement is NOT an option.

But why is the basement not an option? If it's just money, one can always get an underground shelter, which is cheaper than a basement.

What kills people in tornadoes is usually flying debris ... or being turned into flying debris. You need something that will stay anchored and not let branches and shards of rafters penetrate it.

A reinforced concrete bunker like virgilcarter described, tied into the slab or foundation, would be the solution if you are building from scratch and can't do a storm cellar.

We are doing a storm shelter/safe room in our new house. You can go to the FEMA website to see their specifications on a storm room. For example, I think we're having like 8" concrete walls, the door needs to open inward so debris doesn't lock you in room, etc. PS - I live in TN and unfortunately severe weather is a possibility for tomorrow! :( I think it's great your doing a storm room!

southermum - is yours in your basement?

Our master closet is going to be our storm shelter, similar to what virgil described. Our exterior walls will be ICF as well as all the walls of our closet. The crawl space below the closet will be filled with concrete and it will have a concrete slab for the ceiling. The door will be steel, trimmed out to look like the other interior doors. We lost the windows that were originally in the closet, but this was the best room to make the shelter. Even if the rest of the house wasn't ICF, we were still going to make a shelter this way regardless (we live in North Alabama).

I like the idea of using the 'concrete reinforced walls & ceiling, and steel door that opens inward' in a closet and that it still looks like a closet. We'll be having two large master bath closets and one is in the interior -- no outside walls -- so that seems like a good location.

Thank y'all for your suggestions... links. Exactly what I needed to further my research.