The paper addresses the design of large roof structures for semi outdoor spaces through an investigation of a type of performance-oriented design, which aims at integrating performance evaluations in the early stages of the design process. Particularly, aiming at improving daylight and thermal comfort under large structures, the paper focuses on the exploration of passive solar strategies to reduce the need for imported energies. Referring to this context, the potential of parametric modelling is investigated with respect to performance-oriented design and a method, denoted ParaGen, is presented, based on the integration of parametric modelling and genetic algorithms. The potentials of the method are shown by discussing a case study, the roof SolSt. The design process of SolSt is based on parametric variations of its curvature, the density of its modules and the geometry of its cladding and explored based on the daylight and solar exposure of the covered spaces.