using a 2nd hand spiral staircase

[John ONeill]

I'm about to buy a 2nd hand really cool spiral staircase- it's only 6'9" tall but the shed can only go up 15'. So I'm thinking a good halfway mark would be 7'3" to start the 2nd floor (2x6 for floor).
That would mean that I need to add 6" on top of my existing concrete slab.

Does anyone have any ideas or suggestions? Add add'l 6" concrete -vs- wood?

Also this is 1 piece that's 5' diameter- can this fit through my 3' wide door if I "corkscrew" it ?

Thanks!
John O'Neill

 

[gregers]

maybe make up a reinforced pad stone?then wrap it in skirting board.