The cages are made of a few small brownish-red rectangular cages. The small cage is made of two cages with another on top of them. The large cage (large) is made of six rows of two cages on top of each other with another cage on the top and a beat-up gray cloth. They are usually found in raider or super mutant camps.
The cage is located under Raider → Miscellaneous in the workshop.
Cage (small) (1)
Cage (large) (1)