We developped a 3D Monte Carlo Lyα radiation transfer code to understand the diversity of Lyα line profiles observed in star forming galaxies and related objects (Verhamme et al. 2006). Our code allows for prescribed arbitrary hydrogen density, ionisation, temperature structures, and dust distributions, and arbitrary velocity fields and UV photon sources.Here we present results from the first modelling of the Lyα line and of the UV spectrum with our code of a sample of z ~ 3 Lyman break galaxies observed by Steidel and collaborators (Pettini et al. 2002) and taken from the FORS Deep Field (Tapken et al. 2006). A simple model of an expanding neutral shell surrounding a starburst region can reproduce the whole variety of spectra ranging from double-peaked profiles to asymetric emission lines, P-Cygni profiles or broad absorption. The main determining parameters are the outflow velocity and the dust content. Other parameters such as the hydrogen column density, the intrinsic Lyα emission and hence SFR, and the intrinsic Lyα line widths can be determined consistently taking all radiation transfer effects into account.