Safe room

[slownsteady]

I'm guessing the height of that porch is about 3 ft. which means you'll have to excavate if you want room to stand up. Be mindful that you would have to be sure not to disturb the porch footings. I can't tell from the pic how wide the room would be (front to back).
Can it be done? Sure.
Can you do it yourself? I guess so.
Will you be taking on a BIG project? You betcha.
Is it worth the effort? depends how much you need it.

 

[mudmixer]

For an addition source on safe areas, looking at the FEMA standards for a "Safe Cell" that is designed for life safety from tornadoes. The largest cause of deaths is from fragment impact and this standard addresses that for use in many situations from isolated below grade, isolated above grade, built into new construction as a bathroom or closet or added to existing home. Basically it is a 8" reinforced concrete block box with a concrete slab for a top that can be built for many applications. Steel and wood are not compliant.

Obviously, the door is steel and opens inward for egress since debris and cars can eliminate the exit from opening. Wood offers little reliable protection.

Dick

 

[frodo]

My opinion, since its your foundation. I would hire out the foundation work.

it is a skilled level job. not only the building of it,

but the excavation and back fill compaction are very important