Think in routes, not in single toys
A rat cage works when a rat can travel from floor level to the highest corner without a leap he has to guess at. Before you hang anything, stand back and plan routes: a shelf up to a hammock, a rope from that hammock to a higher perch, and a second way down that does not retrace the first. Rats are bold climbers, but they still fall, especially youngsters showing off and older rats whose back legs are less strong than they were. Every route you build should have a soft or solid landing underneath it.
Use a tall barred cage with narrow enough bar spacing that the smallest rat cannot squeeze through, and solid shelves or covered levels rather than bare wire underfoot.
Hanging hammocks so they hold and invite
Fit at least two hammocks, at different heights and in different corners, so the group can pile in together in one and a rat who wants space has another. Clip all corners to the bars with metal clips or hooks that rats cannot chew through, and hang the fabric with a gentle sag rather than drum-tight. A hammock pulled flat is hard to climb into and uncomfortable to sleep in; a hammock with a pocket invites the whole group to pour themselves into it.
Fleece is the usual hammock fabric because it does not fray into long threads that can catch toes. Inspect edges weekly. Once teeth have opened a hole with loose loops inside a double-layer hammock, retire it, because a rat can push his head through an inner hole and become trapped while you are asleep or out.
Rigging ropes as climbing highways
Choose thick cotton or fleece-wrapped ropes that rat feet can grip, and run them diagonally rather than vertically, so climbing is a scramble and not a chimney climb. Fix each end firmly to bars or shelf edges and tug hard before the rats are allowed on it; a rope that gives way mid-climb teaches a rat to distrust every rope after it. Replace a rope that has been chewed thin in the middle, and wash or swap ropes that have absorbed urine at the low ends.
Cross one rope over another to make a junction rats can pause on, and place a chew toy or a small forage wrap at the far end of the longest route for the first few days. Rats repeat journeys that ended well.
Levels, litter, and the ground floor
Keep the floor for what belongs there: a deep layer of suitable substrate for digging, a litter tray in the corner the rats already favour, food and water that cannot be knocked from a height into the bedding, and a solid hide where a rat can be on the ground and out of sight. Water bottles fix to the bars at a height reachable from a shelf as well as the floor, so a rat does not have to complete a full descent every time he is thirsty after a nap.
The weekly refit
Hammocks absorb urine quickly and are the main source of cage smell, so swap them on a short rotation rather than waiting for a full clean. Bag the used set straight into the wash, wipe clips and rope fixings, and refit using the layout the rats already know. Change one element at a time when you improve the setup; a whole new cage geography in one afternoon leaves even confident rats cautious for days.
Family members picked by the owner may open the profile for these rats once access has been granted under KinsLe Family Sharing.