Large size multi-gap resistive strips Micromegas have been chosen together with the small strips TGC (sTGC) to be mounted on the New Small Wheel (NSW) upgrade of the ATLAS
Muon Spectrometer. The NSW is the most ambitious and challenging upgrade of the ATLAS experiment for LHC-Phase1 (the current long shutdown) and will exploit its full capabilities after the Phase2 upgrade of LHC when the luminosity will reach values up to 7.5$\times$10$^{34}$cm$^{-2}$s$^{-1}$ severely impacting on the ATLAS muon forward reconstruction and trigger. Four types of large size quadruplets Micromegas detectors are currently in series production in France, Germany, Italy, Russia and Greece. At CERN the integration of the modules and their assembly in sectors composing the wheel is well advanced. All the procedures of quality control are in place and steadily running. In this presentation the main challenges of the project will be reviewed. The achievement of the requirements for these detectors revealed to be even more challenging than expected, when scaling from the small prototypes to the large dimensions. We will describe the encountered problems, to a large extent common to other micro-pattern gaseous detectors, and the adopted solutions. In addition, the work of the integration of the detectors at CERN and the results from the validation tests at CERN on Micromegas sectors in their final configuration, will be also presented.