Welcome to the site John! Fill out your profile so everyone can see your rig and help out alot more. But in this case, what do you want to put on this rack? A few snowboards, maybe a surfboard every now and then? Then you can go with a simple rack that sounds like your thinking of mounted straight to the fiberglass top with some rubber bushings and fenderwashers. Now if your thinking of putting your spare up there or something heavier than a few pounds your looking at building a full metal structure to go over the roof to support the weight since the hard top will break instantly.
DD- 1995 YJ 2.5L, Cat delete, 19lb injectors, 30/9.5r15
Trail Rig- 1994 YJ 4.0L, Rubicon Express 4.5inch lift, 1inch body, D30 Aussie, 33/12.5/r15 Cooper Mud Terrains, front bumper, rocker guards