My RIR's have no problem getting up to their roost which is about 4 1/2 feet above the coop floor. Their nest boxes are only about 18" off the floor. Edited to add.... Welcome to BYC! It's been a wealth of information for me as I'm a novice at chickens and ducks.
RIR can handle three to four feet no problem. Make sure roosts are higher then nest boxes. I have my nest boxes starting at 30 inches and this is for selfish reasons. I don't like to bend over to collect the eggs.
I' m in the process of building a new coop and am placing the outside collectable nestbox about 14 inches off the floor. This makes it a height outside that my gkids can collect those eggs. They just love gathering the *chicken eggs*. I don't mind bending a bit to collect them if it gives my gkids wonderful memories! I still remember collecting eggs from my friends grandmother when I was about 6. Made quite an impression!~
