In the view of the high luminosity run of LHC from 2015 onwards, during the last two years (2013/2014-Long Shutdown LS1) one of the major upgrades of the CMS experiment is completing and improving the muon system performances by installing a fourth layer of RPC detectors in the forward region. The fourth trigger station (on two new endcap disks) consists of 144 double-gap RPC chambers, which are assembled and tested at three different production sites-CERN (Switzerland/France), Ghent (Belgium) and BARC (India). The complete chamber construction, quality control procedures and preliminary results are detailed here.
