Large area catalogs of galaxy clusters constructed from ROSAT All Sky Survey provide the base for our knowledge on the population of clusters thanks to the long-term efforts on their follow-up. The advent of large area photometric surveys superseding in depth previous all-sky data allows us to revisit the construction of X-ray cluster catalogs, extending it to lower cluster masses and to higher redshifts. We perform a wavelet detection of X-ray sources and make extensive simulations of the detection of clusters in the RASS data. We conduct photometric and spectroscopic identification of our sample using SDSS public data and own programs within SDSS, extending RASS cluster catalogs to a redshift of 0.6. We show that there is no obvious separation of sources on galaxy clusters and AGN, based on distribution of systems on their richness. We conclude that optical cluster richness has to be included in the modelling of cluster selection function. Optical identification results in a substantial change in the expectations for detectability of galaxy clusters at X-ray. We show that cluster X-ray shape influences the X-ray cluster detection and report the results of the full modelling of the cluster selection function. We discuss the redshift evolution of the high end of the X-ray Luminosity function and provide a comparison of our sample with the currently discussed parameters of the LCDM model.