The decision support systems regarding the Supply Chains (SCs) management services can be significantly improved if an effective viable method is utilised. This paper presents a robust simulation optimisation approach (SOA) for the design and analysis of a granularity controlled and complex system known as Consumer Supply Network (CSN) incorporating uncertain demand and capacity. Minimising the total cost of running the network, calculating optimum values of orders and optimum capacity of the inventory associated with each product family are the objectives pursued in this study. A mixed integer nonlinear programming (MINLP) model was formulated, mathematically described, simulated and optimised using Genetic Algorithms (GA). Also, the influence of the problem's attributes (e.g. product classes, consumers, various planning horizons), and controllable parameters of the search algorithm (e.g. size of the population, crossover rate, and mutation rate) as well as the mutual interaction of various dependencies on the quality of the solution was scrutinised using Taguchi method along with regression. The robustness of the proposed SOA was demonstrated by a series of representative case studies.