It isnt a carrier, like a safari rack, if you want to make one jst basically make a 36" x 36" H out of square steel, and make the crossbar on the H of flat steel. Drill through the 4 corners of the H into your stock rooftop bars, after placing them the correct distance apart... and then drill holes to mount the crossbar. Then in the middle of the crossbar, drill a hole for a long threaded bolt that will reach all the way from the bottom, through the wheel... grab a circular saw, make a 6" circle to place over the wheel, drill through the center of that, place your long bolt through the bottom of the crossbar, up through the center of the rim, through the hole in the circle, and top it off with a wingnut or the stock lastic halfmoon, or any other nut youd love... i added a cargo net over it all for looks, and so i can carry crap in the wheel, bc i mounted the rim and tire upside down(i just prefer the majority of the weight closer to the vehicle.
1994 Bright White ZJ... 4" driving lights, and custom rusted rear hatch mod.
If this is a Jeep thing... I hope someone understands.