Use this procedure to change the thickness of a slab or roof slab for which the Base Thickness (BT) variable is used to define the Thickness value in the object style. If the style specifies a fixed thickness for the slab or roof slab (or for any component of a multi-component slab or roof slab), then the Thickness value on the Properties palette is read-only and can only be changed by editing the style or applying a different style.