On Kawasaki Mules we took a piece of strap steel about 1/8" or so thick by 4-5" wide and long enough(24+") to span from top of front roll cage to back of roll cage. We bolted the Big Sky to it then the strap steel was bolted to the roll cage. The mule roofs we had made out of aluminum. We could unbolt all the add ons then move them to a new Mule when they were bought. This pic shows how the gun boots were mounted on the Mules.
Here is how I mounted the Big Sky on my old Ranger to the steel roof. The other pic is how I mounted the gun boots on the old Ranger. I did the same on my new one with both.