Robos are the smallest of the hamsters but don't really require any less space than the rest. The biggest cage that you can afford is still the best. They tend to be very active and run around a lot, especially if you do not provide a wheel. There were earlier concerns that the bars of some cages were too widely spaced apart but most hamster cages are suitable for roborovskis. Cages for guinea pigs and rabbits would obviously not be.
See also Comparison of a few types of cages