This is an example of a hen roost. Here a simple drop cloth is used rather than a removable ‘poop’ board. The dimensions are 18 inches apart and 18 inches high above each rung. This spacing allows for birds on the lower roosts to avoid being pooed on overnight.
This one, with no overhang on the ends, also allows for proper angle of each individual roosting bar. 2 screws into each end and voila!