Most people either use something like what is shown above, or mount traditional off road lights to a roof rack or basket. You really don't want to mount the lights directly to the roof of the truck. The metal isn't really all that strong, and I can just about guarantee that they are going to leak.
If you do a lot of highway driving, I would tend to shy away from roof mounted lights, you will almost certainly have to deal with a lot more wind noise and drag. The previous owner of my truck removed the roof basket and all 5 7" lights because he said he couldn't stand the noise.
And finally, check your local laws. Some states require that those lights be covered for on-road use. It can be a real pain to cover and uncover those lights all the time. It can be an even bigger pain to keep getting tickets for it.