If it is the development of the stringer that you draw directly, to fold it you will have to draw exactly the fold lines and insert folds with angles to be filled in! for right-angled pieces it's easy but for a stringer where I think there will be regular curves it becomes a little more laborious!! It is better to go straight to the sheet metal work!!
In fact I was sent the outline of the stringers unfolded in . DXF, so I opened a drawing with the drawings and simply copy/paste in sketch to finish with an extruded base/boss.
For the moment I only have an unfolder without sides and for simple information a radius and a distance (see sketch image).
At this point, you can maybe use the winding function to project this sketch on a cylinder that has the radius of the finished part, and it can be a good basis to work on to go to sheet metal afterwards!!
I don't know solidworks and therefore I can't help you with the software (I work with Inventor).
First remark on the drawing of the sketch, it is composed of two straight parts (at the beginning and at the back) as well as a wider part in the middle.
This makes me think that we are in the presence of a spiral staircase and not a spiral staircase, otherwise it would simply be of a straight line.
Could you give us a little more information about your staircase (seen from above for example).
Otherwise I work as a draughtsman/coceptor in a factory that makes stairs so I could certainly help you to draw it.
at the sight of your unfolded plan, and at your explanations
You say you have odds if you are on the right scale one is enough
I think that your discontinuous line corresponds to your 1/4 rotating therefore your 1/4 circle
to know if it is the internal or external silt
the width of your staircase between stringers
the height of it
the angle of it
so yes as Be3 says you can copy this part and roll it up on a circular section of a perimeter corresponding to 4 times the length of your discontinuous line via the appropriate tool show in its jpeg
and the same on tangent perpendicular planes for the straight parts
you converted the whole thing into a 3D sketch
then you make a shift
for the rest the threads on the site talk about it and have already been developed