That will be a one off piece. We have no idea how much support there is built into the glass topped table(might collapse under the weight of a topper).

Type of wood? Basic color? Basic design(beyond round)? Plywood? Solid wood? That kind of info.

In addition, you will need to watch the overhang on a non-attached table top. Putting a 6' diameter table top on a 3' diameter table and having Uncle Harry put his elbows on one edge to boost himself out of the chair could either wobble the whole top, or have it come crashing down.