Fabricate a frame that will hold the top of the marble desk. A rectangle of 2-by-4 beams around the outer edge, with beams going across, as well, is good. Use at least two wood screws to fasten these pieces together at each intersection.
Drill holes into the marble. While drilling, keep the bit wet with the spray bottle. Be careful not to drill too deep, so as not to go through the other side. Use a bit that is slightly smaller than the masonry screws.
Attach the frame to the marble top, using the brackets. Depending on design and skill level, consider building a drawer section underneath the desk. Build legs in a style that matches other furniture in the room. Sand and varnish the finished wood parts.