Could they and would they.
This lot are about twenty feet above ground level. They are bantams.
I've had bantam/dual puropose crosses do much the same.
My friends Fayoumies roost in his open loft 3 stories up.
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What I've found is the chickens that can get to high places tend to fly up in stages if the can't make the jump in one.
Some chickens can get to roost spots in high places and others not so much. A lot I think is going to depend on the breed of the chicken.
I'm not convinced that a ramp is going to make things any easier. Even a ramp leading from ground to a pop door in a raised coop (3 foot off the ground) is rarely walked up by adult chickens. They usually hop on at some point along the ramp, even the heavier breeds.
You might get better results by providing jump platforms or bars which they can jump up from to the next level.
Will they do it? Only a trial and attempted training will tell.