If your truck didn't come with the roof rack...then they are missing the support beams in the roof structure that holds it. You can purchase all of the components to the roof rack and install it...I just wouldn't recommend putting anything up there with a significant amount of weight as you may be disappointed with a possible roof collapse!
Here's a link to the parts of the roof rack that you can order from Fontana Nissan:
Nissan Performance Aftermarket Parts | Nismo | Nissan Racing Parts
Hope that helps!
Scott
Sorry Scott but I gotta call BS on the support beams in the roof.
there are no cross supports in a hard top LE with a roof rack. There are 4 mounting plates that are spot welded to the roof. those plates have threaded holes in them for the blots that bolt the rack to the roof. They are thin sheet metal and have
0 load bearing support across the roof. You can do what I did and drill 16 holes in your roof use grade 8 bolts with large fenderwashes in the cab with silicone. had it on my truck 3 years no leaks. Or you can do what a few of the KC guys have done and use the mounting brackets and oem bolts.
Also the rack is only rated for 125 lbs. thats not a lot of weight you should never have an issue with a roof collapse. You have the same risk any one else that has a rack has of it collapsing in on it self.
I was the first known truck to do it. It can be done, and successfully as well