In this work, we have developed an algorithm which generates a random packing of irregular sized spheres using the ballistic deposition method. Our aim is to provide useful tools to represent a three-dimensional array of spheres of different sizes that can be used to study the sintering of fine spherical particles. Apart from the well known devices that have been introduced such as relative density, coordination number and radial distribution function, we show how the Voronoi polyhedra can give useful information that can be followed during a sintering simulation. We extend the definition of Voronoi polyhedra such that it will be useful for describing an array of particles of different sizes during sintering.