Extensive computational resources are required to solve large-scale nonlinear problems having a finite element mesh with a large number of degrees of freedom (DOFs). Model order reduction (MOR) is a technique used to reduce these DOFs, facilitating a faster solution with reasonable accuracy. This work proposes a method for constructing a finite element-based Reduced order model (ROM) by extending the method of modal derivatives (MDs) to analyse nonlinear vibrations of geometrically complex thin-walled structures. We show that the use of MDs is an effective method to capture the geometric nonlinearities that are present in the system. After validating results with the literature, the proposed ROM is applied to the analysis of a Miura-Ori patterned origami structure and the results of the numerical simulation are compared to that of experiments.