The India-based Neutrino Observatory (INO) collaboration is planning to build a massive 50kt Magnetized iron calorimeter (ICAL) detector to study atmospheric neutrinos and to precisely determine the neutrino oscillation parameters. About 30,000 2mX2m size glass Resistive Plate Chambers (RPCs) will be used as active detector element sin ICAL. Starting with a small 30cm X 30cm size RPCs, we have now succeeded in developing full size2m X 2m RPCs. The fabrication procedures used for these large size RPCs as well as their performance will be discussed in this paper. We will also present some preliminary results from our studies on SF6 based gas mixtures on the RPC operation and characteristics.