How to model an interior spiral stair in Sketchup

plugins used: s4u stair: https://sketchucation.com/pluginstore?pln=s4u_Stair s4u slice: https://sketchucation.com/pluginstore?pln=s4u_Slice 1001bit pro: http://www.1001bit.com/pro/download.html vertex tools 2: https://evilsoftwareempire.com/vertex-tools/download shape bender: https://sketchucation.com/pluginstore?pln=clf_shape_bender_v055 curve maker: https://sketchucation.com/pluginstore?pln=dm_curve_maker_plugin soap skin bubble: https://extensions.sketchup.com/extension/c8d49537-51db-40a7-ac0e-474a244eb525/soap-skin-and-bubble