Like the others, I offer nests to my birds.
In my experience, societies tend to be more apt to perch at night than other species, like zebras.
I just got another society and she ignores her sleeping nest.
Personally, the only nest-sleeping societies that I've had were birds who were provided with sleeping nests as youngsters, shortly after weaning. I've had lots of young birds who took to sleeping in the food bowl, so I provided a sleeping nest and they used those eagerly.
So I think it depends on the individual in terms of whether they'll prefer a nest.
For my birds, we have sleeping nests and breeding nests.
Sleeping nests are open-topped nests, like a bowl. (I've never had a bird try to roost in one of these; they only sleep in them.)
Breeding nests are the bamboo covered nests, like pictured above. (They'll sleep in these too, of course, but I end up with territorial behaviors and lots of eggs so they obviously stimulate breeding. Whereas I don't see eggs and territorial-ness with the open-topped nests. If you do, then they may not work out well for you. )
For sleeping nests, I make my own. Actual natural fiber nests are impossible to clean and disinfect and I've never been able to find the plastic canary nests in-store.
So I make sleeping nests out of Kool-aid canister caps:
http://tinyurl.com/o5l4fdg
Take the label off, poke 2 holes in the side with scissors, take two lengths of hemp thread. Tie a big knot at the end of each thread and cut off any extra so there's just a little knobbly knot at the end. Thread the strings through the holes (this way, there's nothing to get caught up on, whereas if you take one length of twine and pull it through both holes, then there's twine spanning the holes on the inside of the nest and they could get a foot caught).
The knot should be big enough to prevent the twine from pulling through the hole. Use the twine to tie it up in a corner of the cage.
I line them with paper towel bits to keep them clean. But if your guys toss those, then you can just cut them down and wash them. Easy to disinfect.
These comfortably fit 2-3 birds.
If you go with a bamboo covered nest, I definitely recommend using a zip tie to secure it to the cage. (Wrap around the metal prongs and a vertical cage bar).
I've had birds knock these down multiple times (no idea how), so securing them is a must.
Another idea is a shelf. There are corner shelves and hang anywhere shelves.
Just beware that they tend to run large, with wider-than-ideal spans between the bars, better for larger birds. I've been unable to find one suited to small birds. But I've made up some paper towel sleeves to put over the rectangular shelves.
I took two paper towels for a good thickness, folded them in half and put in a couple tacking stitches on the sides to turn them into sleeves. So they slide over the shelf. It was able to make about 90 in an hour. I thought of running them through the sewing machine, but I didn't want threads in the cage. And I didn't want to make them from fabric as I didn't want the laundry or the risk of toes getting caught in the fibers.
As for a number of birds, I recommend 2 or 4. I don't recommend 3, as in my experience, you inevitably end up with two who favor each other and one becomes an outsider. So I recommend 2, 4 or 5+.
