The paper deals with the optimization of a timber hall structure, designed from timber portal frames, which are connected to steel purlins, rails and façade columns. While the portal frames are made of the glued laminated timber with the rectangular cross-sections, purlins, rails and façade columns are designed from steel I sections. The portal frames are supported by concrete square pad foundations. The optimization of the hall structure is performed by the mixed-integer non-linear programming (MINLP). The optimization model of the hall structure is developed. The objective function defines the material costs of the structure. The objective function is subjected to structural analysis and dimensioning constraints, which are defined according to Eurocode standards. The Modified OuterApproximation/Equality-Relaxation algorithm (OA/ER) and the linked multi-level strategy are applied. With the optimization, the minimal material costs of the structure are obtained, the optimal number of glulam frames and steel members and all standard/discrete cross-sections. A numerical example at the end of the paper shows the efficiency of the proposed optimization approach.