We present here a simple approach to understanding the gas cloud mass distribution
function by simulating formation and destruction of gas clouds and gas
clumps in the ISM. We include as relevant processes coagulation to form
bigger clouds, as well as disruption by collisions and the removal of gas
by collapse to form stars. We evolve initial sets of preexisting gas clumps
with a range of initial distribution functions (flat, Gaussian, fractal)
for their physical parameters, and with different geometrical forms
(spherical or elongated) for the individual clouds, and constrain them within
an imaginary box representing gravitational bounding, applying the kinematic laws of non-elastic collisions. The
results agree well with observations of the mass distribution function of
Galactic giant gas clouds if we choose a Gaussian for the initial distribution
function, and initial gas clouds which are quasi-spherical.