Just having "waves" is not enough for a laser. You need bosons--i.e., quantum particles with integer spin. To see the quantum aspects of gravitational waves that would correspond to this, you would need extremely strong sources--much stronger even than the black hole mergers that LIGO has observed. Nobody has any expectation of observing any quantum aspect of gravitational waves in the foreseeable future, much less being able to control such sources in order to make a laser.