It all depends on the agility of the breed and the height of the entrance. My cochins need a little help
They fly up to the 18" high landing but I have peeps in there now so I added a ramp...now they all use it.
My rosecombs are super agile and can fly up and land on top of the coop. Their door is over 3 ft. high and I just open it and they fly in and out. They originally had a ramp which they never used.It's on my cochin coop now.

My rosecombs are super agile and can fly up and land on top of the coop. Their door is over 3 ft. high and I just open it and they fly in and out. They originally had a ramp which they never used.It's on my cochin coop now.