Having a cage that is big enough for two birds is great if you do not plan to breed, but once you start breeding Zebras you will have to consider that soon you will not have two Zebras, you will have three to six or maybe more. Zebras can breed in small cages, but I do not recommend it. They need the exercise to stay fit and healthy and having a cramped cage is never good. Next the pair will need a place to raise a family. There are several types and sizes of Finch nests available.
Many people use the bamboo woven nests.
I use them lot because they are inexpensive and I can buy them at any pet store that sells birds. The Bamboo nests come in two sizes, regular and large. Both work great. The larger ones are best for birds that tend to have large clutches. Another popular nest is the wooden nest box.