We got a small parrot ladder and put it in with our chicks, setting it up sort of sideways. None have ever used it. They fly over it, or duck under it. But, maybe your chickens will use one. Who knows?
I put one in when they were about 2 weeks old - I found that they couldn't roost on a round dowel but were happy with an 1.5 to 2 inch wide flat piece of wood raised up about 2 inches. Later, as they grew, I added a second, higher one, and they use both all the time.
If you've got the room for it in your brooder box, and if it doesn't make it all the more difficult to clean around, then go ahead. But I don't think it makes a big difference in them learning how to roost later. It's best as a diversion for them, to jump up on & hop down. A piece of branch on the floor will work too. Just make sure it doesn't give them liberty to jump up & out of the box.
Even more than a roost, my chickies love a shallow pan of dirt to dig into & take dust baths in. And a big clump of grass pulled up with dirt & roots & all to peck & claw at.
I used large boxes taped together for my first brooder and cut holes on the sides and slid two smaller dowels thru. It took them awhile but now some are roosting! It's really cute to see! Sometimes it just takes some chicks longer but they will eventually roost,
My brooder is a storage contaner for a patio roughly 2foot x 5foot and 28 inches high but there only 2 weeks old so theres still plenty of room in there even with 16 birds in it. But on nicer days I'm going to put up a fenced in area in the yard so they can roam around a lil more. just thought the roost would give them something to sleep on and hop on and off during the day
My chicks love it. And it helps keep them from roosting on the feeder/waterers. They all seem to just naturally want to be higher. Better view advantage?
I can put my five little ones all on my arm to roost. If it's the highest thing they can see they are content to just sit and snuggle in there as long as my arm can take it. Even when I put my arm back on the floor for them to hop off, it's still higher than the floor so they are inclined to just stay there.