How many roller coasters does Disney have?
The Magic Kingdom has two roller coasters, Space Mountain and Big Thunder Mountain Railroad.
Animal Kingdom has two, Expedition Everest and the Primeval Whirl.
Hollywood Studios has one, Rock 'n Roller Coaster.
The noun 'roller coaster' has no standard collective noun since most roller coasters are not in a group. However, a collective noun is an informal part of language. Any noun the fits the situation can function as a collective noun; for example, a scream of roller coasters, a maze of roller coasters, a park of roller coasters, a tour of roller coasters, etc.