To each their own. Mines below ground. It stays unlocked and supplied. The door can be secured from inside only. I've been thru 2 smaller ones and seen results of 2 of our largest. I've never heard of an EF10 but that's what you should prepare for. This talk of "above ground" shelter might get ya dead. IMO.
You may be late to this party but we've discussed this subject to death. Every above ground shelter that has taken a direct hit from a tornado has survived intact. I've got photographs from all of the above ground shelters in Piedmont that took direct hits from their EF-5 tornado in 2011. Talked to most of the survivors that rode the tornado out and only one had a complaint. And that was about the sound of the roar from the tornado. You may want to do some more research. In the case of a massive tornado going through a very densely populated area you maybe stuck in one of those below ground cubby hole shelters in your garage for a while. Emergency services quickly get overwhelmed. I'd make plans of some type for self-rescue. Otherwise make it comfortable enough to spend hours in. Be aware if you have any family members that have claustriphobia. That's one complaint I heard about the coffin size shelters.