First, set in Options - Current Drawing Preferences - Dimensions the Length Factor to 1.
Now you will get a dimension value other than 0. Length factor is to manipulate the dimension reading for special cases. Normally it should be set at 1, as a cad drawing is normally drawn in real world values, not scaled down.
Then you might have to scale the drawing to get the sizes you really want to have. For instance, what dimensions shall the stairs have?