I am not aware of having to do anything particularly different for a giant macaron than you'd have to do for a regular 1 1/4-1/2 inch type except to pipe them larger. The largest I've seen of the classic kind are about 3-4 inches in diameter. Not sure if you'd have to do anything differently if you want something larger than that. If you want something really giant, just for display, I'd just do a straight stiff Swiss meringue, pipe and shape it to look like a big old macaron and then dry it overnight in the oven with the pilot light.
Anyone else with experience in this area, please jump right in. Good luck, kp!