Chickens can happily roost on sawhorses or chairs or many other kinds of things. Of course these things will get poopy, so be prepared to throw them away afterward, or consider them permanent chicken furniture.)
There are plenty of ways to create enough roosting space buy just propping a long board between two supports (chairs, sawhorses, cinder blocks standing on their ends, and so forth.) Make sure the board will not fall down when the chickens fly up and down (clamp or screw it to the sawhorses, run it through the backs of the chairs or the holes of the cinder blocks, etc.)
You could make a structure like what holds the nests, but a little taller, and let them roost on it without the plastic bins (taller because chickens like to roost on the highest available surface: you want that to be the roosts, not the nests.)