The simulation of large grids requires the generation of grid instances and an approximation of grid components' behaviour. To generate grid instances, this paper outlines a set of high-level properties of grids and considers ways to assign values to those properties. The paper also brings together existing application-level network and host models and discusses how they are used for the simulation of large grids. A grid instantiation is described in detail as part of a master-slave case study, and a large grid is simulated for the evaluation of a variety of scheduling strategies. The case study also motivates a performance prediction method, which is assessed against simulation results.