Spectroscopic ellipsometry has been widely used as one of the metrology methods of choice in various industries: microelectronics, photovoltaic, optoelectronics, flat panel display, etc. We present an example of the characterization of dielectric multilayer structures on the substrates with unintended surface modifications involving macroscopic roughness. We assume that under our inspection conditions, the effect of macrorough surfaces can be treated as the presence of a specially designed overlayer on top of the ordinary substrate. A systematic procedure was then proposed to simulate the dielectric response of the overlayer. This approach is quite useful in a practical sense and provides more accurate process monitoring and control in a production environment.