  Future space missions will improve considerably our understanding of the
formation and history of planetary systems. Currently, observations show that
the presence of planetary companions is closely linked to the metallicity and
the chemical abundances of the host stars. We aim to build an integrated tool
to predict the planet building blocks composition as a function of the stellar
populations, for the interpretation of the ongoing and future large surveys. We
synthesize stellar populations with the Besan\c{c}on Galaxy model (BGM) which
includes stellar evolutionary tracks computed with the stellar evolution code
STAREVOL. We integrate to the BGM a simple stoichiometric model to determine
the expected composition of the planet building blocks. We determine the
expected PBB composition around FGK stars, for the four galactic populations
within the Milky Way. Our solar neighborhood simulations are in good agreement
with the recent results obtained with the HARPS survey for f_iron, f_w and the
heavy mass fraction f_Z. We present evidence of the clear dependence of f_iron
and f_w with the initial alpha abundances [\alpha/Fe] of the host star. We find
that the different initial [\alpha/Fe] distributions in the different galactic
populations lead to a bimodal distribution of PBB composition and to an
iron/water valley separating PBB with high and low iron/water mass fractions.
We linked host star abundances and expected PBB composition in an integrated
model of the Galaxy. Derived trends are an important step for statistical
analyses of expected planet properties. In particular, internal structure
models may use these results to derive statistical trends of rocky planets
properties, constrain habitability and prepare interpretation of on-going and
future large scale surveys of exoplanet search.
