This is a grasshopper definition of the classic 'Spiral Staircase' example. It is structured into two parts. The first re-uses the 'Increment II' design pattern with modifications to the increment values. This first part drives the geometry of the spiral staircase as all subsequent components of the stair are dependent on the initial plotted points. The second part of the definition builds up the details of the staircase - which includes thickening of the steps and handrail.
As the spiral staircase's geometry can be easily described, it is well-suited to be modeled in a parametric environment. The key is to define the parameters that affect form and also to describe the associations between those parameters.
The grasshopper definition can be downloaded here.