The short answer for a first rat group
Buy one large cage. For a first group of rats, a single spacious cage beats a connected multi-cage setup on almost every measure that matters in the first year: the rats get one shared territory they can organise socially, and you get one cleaning routine, one set of doors, and one environment to learn on. Connected setups have a real appeal and a legitimate place later, for experienced keepers expanding a group's territory. As a starting point they multiply exactly the things a beginner is still learning — cleaning, supervision, and managing the group's politics — before you have the eye for any of them.
What one large cage does well
Rats use space in three dimensions: they climb, they need levels at different heights, and they like a choice of sleeping altitudes from a floor hide to a hammock near the roof. A tall, wide single cage delivers all of that inside one territory, which matters because rats are colony animals who settle best with shared scent and shared landmarks everywhere. Practically, one cage means one deep clean on one schedule, one place to scatter food so every rat forages fairly, and multiple water bottles and litter trays placed where the whole group passes them. It is also far easier to make one cage interesting: rotate hammocks, ropes, boxes and dig trays through a single space and the rats get novelty without you re-engineering plumbing between boxes.
Where connected setups cause trouble
The tube is the problem. A connecting tunnel is a bottleneck with one entrance at each end, and in rat politics a bottleneck is a thing to own: a confident rat can guard a tube mouth and effectively tax every crossing, while a rat being chased has nowhere to dodge if the tube is the only route between sections. During the squabbles every young group has, rats can end up trapped in the wrong section, away from water or from the rat they are bonded to. The keeper's side is no kinder — tubes and connectors are fiddly to scrub, harbour grime at every joint, chew into escape projects, and double the surfaces in a full clean. None of this makes connected setups wrong; it makes them a second-year answer to a problem you may never have.
When a connected setup does make sense
There are honest exceptions. If your rats' single cage genuinely cannot fit the room and two smaller units stacked or joined give more total volume, a connection may be the practical route. Experienced keepers also link a playpen or a second cage temporarily to give an established, harmonious group new exploring territory, closing the link at night. The pattern in both cases is the same: the group dynamics are already known and settled, the keeper already reads rat behaviour fluently, and the connection is a bonus rather than the foundation. Notice what is absent from the list — a first group, still being introduced, still sorting its hierarchy, is exactly the wrong population to hand a guardable doorway.
Keeping one big cage clean without drowning in it
The fair objection to one large cage is the cleaning: it is a lot of cage. The answer is to run it as zones rather than as one weekly marathon — litter trays lifted every couple of days, hammocks and fleeces swapped on rotation, levels wiped as they need it, bottles checked daily, and a full strip-down on a longer cycle so some familiar scent always survives. That rhythm is easier to keep when it is divided between the people in the house instead of living in one person's weekend. KinsLe's Care Teams fits the zoned approach exactly: each duty for the cage — trays, hammocks, bottles, the deep clean — can be assigned to whoever helps with the rats, and completed tasks are marked with a timestamp, so a big cage stays fresh without anyone having to remember who did what last.