SO2:Stairway

In the Floor Features, add feature and select the Staircase Preset. All you need is:

Step Count the total number of steps

The dimensions of each tread. This is the width, (Horizontal), and the depth, (Vertical), of the step

Height of each step or total height to define the height of the stairway feature

Height Offset is the base dimension of the first riser. This will allow you to define the landing height of staggered stairways.

Note: Make sure that the ceiling has a void, or make an opening with "Anechoic material" to cope with the staircase opening into another room/hallway.