You can use a bumpmap (imported image map) in the default shader of the object's wall part, or use a PF with appropriate sizes, and use the color(!) of it as input for displacement tab, or feed it with small displacement value into the default shader's input. PF should go through a transform shader set to world if you want world space. If not, it'll use UV space. You need different sizes for UV than for world, as Uv only goes to 1 max. In principle.