The main goal of this paper is to define a design procedure for modular, lightweight and freeform structures by quantifying the relative importance of serviceability limit states and ultimate limit states. The modular building stones of the freeform structures under study are sandwich panels with a foamed polyurethane core and TRC (textile reinforced concrete) faces, shaped in the form of hyperbolic paraboloids (hypars). The shape of these modular building stones allows the production of structural elements on a reusable doubly-curved mould. For the dimensioning of the global modular structure, two states are important according to the Eurocodes: the ultimate limit states and the serviceability limit states. Due to the lightweight aspect of the modular structure, the serviceability limit states will gain in importance: stiffness and crack formation become important factors, as does the influence of repeated loading. These factors and their influence on the final design of the proposed structures will therefore be discussed in this paper.