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 nonelastic 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.