To generate power from tidal forces directly, in a self contained building, you’d want to lift something very heavy when the gravity is “turned down”, and then lower it and generate power when gravity is “turned up”. A building the size of the Burj Khalifa could generate an absolute maximum of around 100MJ of energy, twice daily (two tides), using perfectly efficient machines. However, it is both possible and feasible to harvest the tide for power. Ultimately, all of the energy gained from tidal forces has to come from somewhere, and that somewhere is the rotational kinetic energy of the Earth. So, when you generate power from tides you literally slow the Earth down.