I made a very similar model in graduate school.
Posts about making a model spiral staircase written by david neat
Model making basics includes arches, stairs, circular stairs, etc.
Gallery of Public Bath / Müntinga + Puy Architekten - 16
Posts about model construction written by david neat
assembled steps - seriously in-depth analysis of mini making
Posts about theatre set design model-making written by david neat
marking up a spiral staircase
making an open flight of steps