A versatile model of the surface profile is proposed to include such features as the smearing of the distribution profile near the surface, surface relaxation, long or short range order in the case of solid or liquid metals, respectively. A closed form expression is derived for the spectrum of x-ray reflectivity from metal surfaces which can be described by this model. The spectra generated by a variety of surface profiles are explored by varying the parameters of this model. Particular features of liquid metal spectra are found, and discussed in relation to experimental data. In particular, the model reproduces the recently obtained [Phys. Rev. Lett. 75, 2498 (1995)] reflectivity spectrum of liquid mercury surface, which has two maxima in the range of small and large Q and an intermediate Q "shoulder" The shoulder is shown to be a fingerprint of the surface relaxation.