One Example of a Rat Play Room
In my space I don't allow my rats to free-range. I do, however, want them to be able to run around in a largish space, so I came up with this temporary and semi-portable "room". I devote most of a human room to this thing, but one can always make it smaller too, if moving it or closing it down becomes important.
The most important point: Giving rats a rat room requires 100% supervision of the rats with a human inside. Depending on how busy you make the room (boxes, etc.), they need to be watched and kept safe. Also, in these photos you will see tall piles of boxes, which are unsafe for many rats. My rats have been practicing with boxes and bins, for climbing and balancing, since they were babies. I trained them gradually to build up their muscles and balancing and jumping skills. Please do not put objects in a room for rats to play on if the rats aren't physically fit to keep themselves safe. I would consider this current set up to be ideal for very fit and skilled rats only.
I'm sure that if I just closed the door and left the rats inside, they would instantly decide they wanted out. With me inside, I'm also unclear about why they are this way, but they are completely tolerant of staying inside. They snuffle the edges but make no efforts to gnaw through the cardboard or dig under the edge. My first rats, 4 girls, were in a different rat room set-up with cardboard on only two sides, and wall-walls on the other two sides, and while I didn't have fleece on the floor (had linoleum), I had to watch them constantly or they would dig and gnaw to escape. I don't know if this is a girl-boy difference or a function of the different structures of the rat rooms, or both. In any case the point is that I can't tell you how your rats would do with this structure but supervision is key in any case.
The materials: 8' x 4' double-thick cardboard flats (got mine at local UPS store) (I think UHaul might carry them too?). I bought 12 flats and brought them home on the roof of my car. Still have 2 stored. For this rat room you need at most 6 flats: 4 for the four walls and 2 for the flooring.
I have two flats as a floor because my apartment is wall-to-wall carpeted so I don't want carpet open to the rats, then double-fleece lined inside for their flooring pleasure. The floor flats are positioned to be about 6-8 inches bigger than the dimensions of the room, and the fleece carpet layers go way outside the walls also. That way the carpet is well out of reach of the edges and the rats don't know there is anything different outside the room.
The 6' width is somewhat flexible depending on your space requirements. For the 2 smaller walls, two 8' flats are folded at each end to make a 90 degree angle. You need at least 6 inches for a fold. Each fold is done sharply. I recall I put something heavy and straight along the line where I wanted the bend. To make sure the line was straight I pressed whatever it was in place with my knees, and then pulled fast and firmly and evenly to make the 'break' (bend).
Position the 4 walls in place and clamp the overlapping corners with 2-inch binder clips at the top and bottom. I put two at the top and two at the bottom of each corner for strong clamping power. Ideally you want clean straight lines so that the corners appear seamless (not interesting to rats :).
The flat side that has the door is actually two pieces, one that is the full 4' high, and a 2nd piece that I cut down to make a kind of stall door or gate. In hindsight I might have made this opening much higher - even left it as 4 feet. Not sure why I did it the way I did, actually. Inside I don't put boxes or other objects that the rats could climb near the door, because they do periodically stand up on the nearest box top and stare towards the door opening, and I'm sure if they could reach it within inches they would try to jump. (Evidence!: http://www.joinrats.com/Friends/Gwen/BoyRatRoom/17180589_PmnXxn#!i=1302747309&k=3T7NdSx
Keeping the door closed is also amazingly simple for the 3 boy rats who don't test it. It's clamped at the edge like the other sides, at the bottom, but the top can't clamp because the door top edge isn't in line with the wall top edge. That works okay because on the other side of the door I use one binder clip at an angle to hold the top edge of the stall door against the taller wall, and then set a very heavy object outside the door and leaned against it, which makes the door appear very solid to a rat on the inside. It doesn't 'give'.
I also have objects resting outside some of the walls, lightly against the walls, for basic support, but inside nothing leans on the walls, and certainly not a human. The walls are left untouched because I don't want pressure to cause wrinkles or bends over time. I have noticed that over time the walls can shift anyway as anything touches them. Periodically I have to reposition the walls, usually when I pull up the fleece to wash it.
Below are photos of all aspects of this rat room, with the most current version first and the original construction at the end.
See how this is quite temporary and somewhat fragile, and yet bulky and kind of not easily moved? But it works for me.
The best function of a rat room like this is to toss some loose oat flakes all over the place and watch the rats go into foraging mode. Foraging in the forest - a basic life skill of rats!
(For more ideas, here's another rat room done a different way: http://www.joinrats.com/Friends/Gwen/RatRoom/10568204_JpzKNj#!i=620787830&k=abi4P