Summarize this article:

Retrofitting an existing room in your home or business is the cheapest and simplest way to protect your loved ones from storms or intruders. While building or installing a prefabricated safe room can cost between $2500-$6000, you can retrofit an existing room for a thousand or less. Choose a room that is in the interior of the house with no windows or skylight, and no walls shared with the outdoors A large walk-in closet works well. A safe room needs a door that can withstand high winds or being kicked in by an intruder, and should ideally open inwards rather than outwards in case debris is stacked outside the room during a storm.  Remove the existing door and doorjamb. Replace the doorjamb with a steel one, and reinforce the surrounding wood with steel angle iron (which will prevent the door from being kicked or blown in).  Replace the door with a heavy, solid wood door (such as one sold as an exterior front door for a home) or with a heavy steel door.  Mount it so that it opens inwards rather than out. You can choose if you want to use a traditional deadbolt or a keyless deadbolt. The keyless deadbolt has the advantage that you don't have to find the key in case of an emergency, but can be dangerous if you have small children in your household who may lock themselves inside.  Before installing the new locks and doorknob, reinforce the wood around them by installing steel or brass strike plates, which you can purchase at most hardware stores.  Install the locks so that the door locks from the inside. If it's a traditional deadbolt, be sure to make a copy of the key and keep the keys in two separate but easily accessible locations, where you can find them immediately in case of emergency. If you are adding the safe room to new construction, you can reinforce the walls and ceiling with concrete, chicken wire, or steel sheeting before adding dry wall and paint to the walls. If not, you will need to tear out the existing drywall to reinforce the walls.  The most cost-effective way to reinforce the walls is by pouring concrete into the cavity between the 2x4s in the walls. Then, screw plywood or 1-1/8″ oriented strand board to the 2x4s on either side. You can then cover this with drywall and paint.  You can also screw steel sheeting to the 2x4s and cover with drywall and paint. You will need to use steel sheeting or chicken wire in the ceiling, which can be done from the attic if you're in a one-story home, or applied directly to the ceiling (less attractive, but chances are good no one will be looking at the ceiling of your closet safe room). If you want to create a more complicated or stand-alone structure, its important that it is up to code. If you don't have a lot of experience with construction, you can contact a contractor or local storm shelter company for help planning and installing your project. Ask around for recommendations of local contractors. Ask family or friends who have recently remodeled or done construction work, or contact the National Association of the Remodeling Industry or a local building inspector, who will be able to point you in the right direction.

Summary:
Select your room to retrofit. Replace the door. Install locks. Reinforce the walls and ceiling. Contact a contractor for help.