Shelter sizes depends on how many people you intend to protect. E.g. 4-6 people, 6-8 people, 8-10 people, or even depends on domestic requirement sizes or animal shelter. The material for shelters is made mostly of steel, concrete, fiberglass, or others.
Shelter can be installed underground in yard, under foundation before new construction, dug out under existing home, etc.
Features in shelters are commonly rechargeable battery-operated lights, bunk beds and mattresses, second emergency door, hydraulic jack for door, water storage tank, generator, chemical toilet, entertainment showcase, wired for electricity, phone lines, fire safe, padded seats or benches, carpet, others.