Any storm shelter should have provisions for a large hydraulic jack and blocking material.
That's one of the things that should be in there as well as a weather radio, emergency lighting, and other supplies.
Even if it's outside, you may have crap land on the door.
I don't have one in this new house. But probably will in a year or so. We'll probably put a hidey hole in the garage.
The last one I put in was a concrete monolithic pour storm shelter. It was 6'6" tall, 8 ft x 12 ft, with a 16 ft by 24 ft patio on top of it.
IF I had had this house built, I would have put one up as a closet within the house. Concrete filled blocks witha slab on top. Steel doors going into the closet with several dead bolts into a steel frame.
The precast ones they set in place with a small track hoe are good. They are inexpensive, don't leak like a poured in place cellar, and go in in a hurry.
They're just small and not attractive.