As the keeper of 5 y.o. and nearly 8 y.o. hens, (with baby chicks on the way) I'd recommend having at least one adequate length roost for chooks who want the option of ease of access. Yes, most chooks can flap themselves up to a 3' tall+ roost, and may like it up there, but it is nice for them to have a roost that requires less energy expenditure sometimes. A variety of heights, IMHO, allows for youngsters and aging hens to be comfortable. Stairstep, ramp, whatever means to get to the roost they want is a nice option for them to have.