Dude, why did you make 2 different topics for the same thing?
Go in the editor on the ride that you took that screenshot and check it out for yourself. Its just wooden beams placed very close to eachother. You can make tunnels like that just using supports.
^They weren't catwalks, they are custom flatboards. It takes a lot of time to put one of those roofs together (if you want an excellence in quality) and you have to be good at using custom beams and putting them together.
Yea. Make one topic. Edit it if you need to add something more discriptive, but just because no one replies to the first one doesn't mean you can go create a second topic about the same thing. If you do this again, you will recieve punishment. This is your warning.