If you get extremes in weather, such as very hot or cold or very humid/wet weather, you'll really want more ventilation in that coop...lots more. Chickens on a roost create a lot of heat and humidity and when the temps drop below freezing, their own humidity and breath will condense on their combs, wattles and even on their bodies and cause frostbite and chilling there. For hot weather, that airless box will just be stifling and also needlessly stress the bird's system.
Ideally, air flow in at the bottom and stale air out the top of the coop...a passive air flow to remove the humidity from the coop will help them stay more comfortable, not to mention prevent disease transmission among the flock. Putting in roosting bars instead of platforms will also aid in the airflow around the birds, moving their humidity and stale air that much better. Nothing at all wrong with round roost bars...most of mine are fat and round, which mimics a bird's more natural foot position while sleeping on a roost.
You could also think about a deep litter system in the run area if you'd like to avoid a muddy, stagnate run and an overload of fecal matter causing harmful bacteria and fungal growth in the soils there. You can use a variety of materials for a better result, as using all of one type and size of material doesn't allow good air pockets into the litter pack, but just build it 6 to 10 in. deep and keep adding as needed to keep a spongy litter pack underfoot. This will keep the soils under your run from becoming too compacted for drainage and also allow the nitrogenous fecal matter to bind with carbonaceous materials instead of overloading the soils there. Over time you can scoop out this rich compost for use directly onto the garden.
Both of these steps can help your chickens live a better and healthier life there.