Addition for Staircase

[offthegridcortland]

Hi all.  I own a small beach-type house where the primary (kitchen, living area) house is on the second floor, built up on concrete pillars with what might be considered a carport beneath.  Before I bought the house, half the lower area was enclosed to create a large bedroom, bathroom master suite.  The lower area is a concrete pad.  The only stair is exterior so you have to walk outdoors, through the weather, to get to the master suite or to the laundry which is in the existing carport area.

What I want to do:  enclose the remaining carport area to create a unified house with interior stairs, a laundry room, and a ground-floor entry to the house.  The enclosure is relatively straightforward, but the total project poses two problems I'm not sure how to solve.  The first I think is relatively simple.  The second maybe a bit more tricky.

Problem 1.:  The carport floor is partially graded, (say 3-4" over a ten foot run) for drainage and that 15' wide x 10' long section will have to be leveled so I can floor the entire area.

Problem 2.:  The stair.  There's no good place to put it without destroying most of the room upstairs and a straight run stair mimicking the outside stair will cover windows once enclosed, so I want to build a small addition on the side of the building, say 6'x6' and two stories high for a spiral staircase from the new, downstairs room to the existing upstairs doorway.  The problem is that there is no foundation present for this addition.  I can think of three solutions.  A) Pour a slab-type foundation for the addition, anchoring it to the existing pad.  This seems frought with problems and settling issues.   B)   Use a footer, post type of foundation and accept that there will be some settling issues and allow for that by using making finish work at the joints of the two structures (not that excited by this idea).  C) Run joists from the existing pad, anchored into the concrete, and cantilevered over the six foot run where the stair case would be.  Kind of a long cantilever, but I thought between this and joining the exterior wall, I might have enough strength.

I know it's hard to visualize what someone is asking with just words.  I hope I have given you enough information to see what I'm asking.  Thanks in advance.  -Aaron