What parts do you need help with?
Switching from chains to cables in the building of roller coasters was important because cables are less likely to snap when hauling several tons of roller coaster cars full of people. Chains are made of linked, welded pieces of metal that can easily snap if they pull too much. Cables, while they can snap, are much less likely to do so, because they're a stretch of fibers, be it metal or other, without any potential weak spots.
