safe room

I just purchased a new home in MO and plan to construct a "safe" room in the, as yet, unfinished basement. I've selected an inside corner area and that's as far as I've gotten. Of course two walls will be poured cement... what should I construct the other two from (and ceiling)? Going through...

I live in Tampa but not in an evacuation zone, so flooding (including run-off) is not a concern. If a hurricane comes, I'll hunker down at home. My home is reinforced cinderblock built to 1999 code, and I feel relatively safe here. But there is no interior room or closet large enough for 12...