Whenever anyone asks what they can do to upgrade their hamster cage, I always say, get some platforms! Platforms help maximize the space by giving your hamster burrowing room AND space on top of that for additional enrichment like hides, sand baths, etc.
You will need 650 sq inches of unbroken floorspace (not a bunch of cages connected!). Smaller hamsters do not need smaller spaces- Roborovski hamsters are the smallest but can also be the most highly active.

- Stack two aquariums vertically with connecting tubes, creating a massive two-story hamster mansion with twice the living space. Secure the top aquarium on a sturdy table or custom stand directly above the bottom tank for stability. Install tube systems connecting both levels, allowing your hamster to travel between floors like a hamster elevator.

Moving forward, it's essential to keep these visual contexts in mind when discussing Hamster Cage System Building For Small Spaces.
- Before deciding to go this way, read through to see what else your pet hamster needs and see what size to build so as to fit all the required accessories. See video of an example of a DIY cage. ... Try and get the larger size; you can even purchase two small or large ones and join them to create more room for your hamsters (if you do this you will have to modify the joining walls/sides)