One of the main issues in the WDM PON networks design is the optimal dimensioning of the network. The network size usually depends on the traffic demand and the user density, taking in to account the active and passive equipment capacity and some physical layer constraints like the attenuation in the optical path. However, some physical layer limitations related with signal transmission in an optical fiber become more relevant in a WDM transmission and when operating at very high data rates, like 10 Gbps or beyond. In this paper we propose a novel physical layer restrictions based integer linear programming (ILP) model for greenfield next generation 10 Gbps WDM PON network design. The results of the model are validated by means of computational techniques. The proposed ILP model takes into account not only the attenuation of the signal in the optical path but also, through the use of the data obtained by simulation software. We take in to account the restrictions imposed by other phenomena like dispersion, cross talk and some non linear effects typically present in a dense WDM optical transmission.