  A full-size prototype of a Micromegas precision tracking chamber for the
upgrade of the ATLAS detector at the LHC Collider has been built between
October 2015 and April 2016. This paper describes in detail the procedures used
in constructing the single modules of the chamber in various INFN laboratories
and the final assembly at the Laboratori Nazionali di Frascati (LNF). Results
of the chamber exposure to the CERN SPS/H8 beam line in June 2016 are also
presented. The performances achieved in the construction and the results of the
test beam are compared with the requirements, which are imposed by the severe
environment during the data-taking of the LHC foreseen for the next years.
