The design of multi-materials requires the determination of several variables: morphology, components and geometric parameters. Previously developed methods help designer making these choices separately because they always lie on a reduction in the number of design variables, as some of them are fixed at the beginning of the study. This paper proposes a method to carry out the simultaneous definition of all these variables in a preliminary design step. The beginning of this work consists in the formalisation of the multi-scale decomposition of the architecture materials. This outline is a guide for the use of databases of materials and architectures, whose combination enables the generation of multi-materials. Within the huge solution space resulting from this approach, a genetic algorithm allows to find optimised materials to fulfil a set of requirements with a limited number of calculations. An analytic example illustrates the efficiency of this method and shows it can provide designers with several propositions of materials.