We investigate the surface roughness influence on the gain from parametric amplification in nanoresonators in the presence of thermomechanical and momentum exchange noise. The roughness is characterized by the rms amplitude w, the correlation length, and the roughness exponent 0. <H <1. It is found that the gain strongly increases with increasing roughening (decreasing H and/or increasing ratio w/xi) due to the increment in capacitive coupling, which plays a dominant role when the intrinsic quality factor Q(in) is comparable or lower than the quality factor Q(gas) due to gas collisions. However, for Q(in) >> Q(gas), the influence of surface roughness on the gain strongly diminishes.