I think it means make a larger bin cage
A bin cage is just a large plastic storage bin - you cut out panels on the front, back and top (using a hot knife usually) and fix mesh to those cut out panels for ventilation. Then it's a cage. You don't want small bins stacked on top of each other, as Amityville says. One larger floor area is better.
Then the substrate goes in the base of the bin - minimum3 to 4" but ideally 6" or more so the hammy can dig tunnels and burrow. It's a tank basically when it's finished.
Here are some examples
https://www.google.co.uk/search?q=la...CFAVkQ_AUIBygC
One larger one is better than two smaller ones on top of each other - especially when a hamster gets older and can't climb.