Well, 1 ft is about right for how Jefferies saw things. But even at 1 ft thick, how would the floor of Deck 5 at -10 only be 7 ft heigh? When I subtract 1 from 10 I get 9. And that would only be in the outer edges, towards the core you get the higher ceilings (as the floor of Deck 4 is 12 ft above the floor of Deck 5).
From the show, I'd guess the hull thickness to be between 8 to 12 inches...
...which is about what we see for the shuttlecraft too.
As for deck heights... the highest ceilings shown were in the corridors and sickbay, but most other rooms were lower (with structural members often being seen).
You're correct I was looking at deck four and five and did the mental math backwards. You'd have nine feet outboard and 12 feet inboard. That's embarrassing