We study the temporal evolution of the Halpha, Ca II 8542 and Na I D1 spectral line profiles in three different flares using high resolution observations obtained with CRISP at the Swedish 1-m Solar Telescope and IBIS at the Dunn Solar Telescope. The observations are combined with realistic radiative hydro-dynamic flare models obtained with the RADYN & RH codes in order to disentangle the physical properties of the flare chromosphere. We show that the asymmetries and central reversals of chromospheric line profiles can provide important diagnostics of the flare properties. These include the evolution of velocity and temperature structures and the non-thermal heating processes during the flare event. We also use the non-LTE algorithm NICOLE to invert chromospheric line profiles and recover the temperature and velocity stratification of the flaring atmosphere.