A perch is their natural way to sleep, and if you make it out of the flat side of a 2x4, they can sit on their feet in cold weather and not get toes frostbitten. But they can survive without one. Take a look at Patandchickens' BYC web page.
Some people clean the coop once or twice a year! Instead, they add litter as needed, over the old, and stir it around, maybe add DE or pelleted lime or something to the litter to keep odor/ammonia down. Lots use a dropping board under the roost because it's easy to dump/scrape the poo off and about half the poo lands there, so that cuts way down on the mess.
You will know you need to clean for sure if you smell any ammonia; those fumes are rough on their lungs.