Random non-uniform solids within a bounded domain

I am new to stack overflow and would like to know how to generate a random distribution of cylinders in a bounded square domain.

The idea is to generate a random distributed solids within the porous media with different radius and relate the distribution with the a factor named porosity.

It looks easy for me to understand step wise procedure but difficult to implement it.

1. create a rectangular domain.
2. define the porosity(vol. of pores initially set to zero and taken as a read data from the user runtime). {vol of pores/ vol of square domain}.
3. generate random distribution of cylinders bounded within specific radius to fit the input porosity value.

Could anyone give a hint on how to proceed and which utility to use please!

Thanks;

Saideep