Experiments play an important role in parallel and distributed computing. Simulation is a common experimental technique that relies on abstractions of the tested application and execution environment but offers reproducibility of results and fast exploration of numerous scenarios. This article focuses on setting up the experimental environment of a simulation run. First we analyze the requirements expressed by different research communities. As the existing tools of the literature are too specific, we then propose a more generic experimental environment synthesizer called SIMULACRUM. This tool allows its users to select a model of a currently deployed computing grid or generate a random environment. Then the user can extract a subset of it that fulfills his/her requirements. Finally the user can export the corresponding XML representation.