35 C = 95 F
5 C = 41 F
Cold is not your enemy, heat is. I’ve seen chickens sleep outside in a tree in weather below zero Fahrenheit, (- 18 C). As long as they are not in a direct wind they do fine. Your temperatures don’t even get below freezing. Cold is not your enemy. At 5 C they will be very comfortable.
That heat can kill them. Chickens don’t sweat like we do. They get rid of excess heat by breathing (panting) and the blood gets close to the surface of the comb and wattles so they lose a lot of heat like that. In the heat their feathers are not as thick as they are in colder weather so they don’t have as much insulation from feathers as cold weather birds.
What you need in a coop depends some on your management techniques, but in general all you need is nests, roosts, protection from predators, and protection for the environment. For your six hens, two nests will be plenty. The minimum recommended size is 30 cm x 30 cm but I personally like them to be a bit bigger, say 40 cm x 40 cm. My hens like to lay together, sometimes three are on the nest at the same time, even if empty nests are available. The extra room makes them a lot more comfortable. Also my hens hatch eggs. The larger nests have some benefits for that.
Chickens like to roost as high as they can so it is important the roosts be higher than anything you don’t want them to roost on or in. Since they poop a lot at night, you don’t want them pooping in the nests. The way I determine roost height is to determine the height of the floor including any bedding, then determine where my nests go, then make the roosts about 30 cm higher. That should be enough height that they prefer the roosts. Don’t make the roosts any higher than you need to. While your hens should have no problem flying up to a roost over two meters high, the higher the roosts the more clear space they need to land without hitting something on the way down and the more room they need to spread their wings and fly up. Also some chickens can be brutes and bullies on the roosts. Sometimes this bullying is so bad that the chickens being bullied seek out a safe place to spend the night. That can be your nests. So be generous in your roost space. Instead of thinking about a certain length per chicken, think more of giving them enough room to get away from a bully if they need to. With your six hens all the same age that should not be a big problem but I’m a believer in providing extra space.
All of us have different predator pressure. I don’t know what your highest risk comes from, quite likely dogs, either wild or someone’s pets. Chickens are prey animals so many different animals enjoy eating chicken. Some will eat the eggs too. While chickens are at risk from predators any time, day or night, they are more at risk at night. Some predators are more active at night when you are asleep and there is no human activity to frighten them away. Chickens are pretty helpless in the dark so they make easy prey. I use a strategy of keeping them somewhat safe during the day but locking them in a very secure coop at night. Others use different strategies with varying levels of success.
I don’t know how much rain you get but you don’t have a lot of environment to protect them from. A wet coop and run is a dangerous coop or run. With all the chicken poop mixed in the floor or ground, a wet coop or run is a breeding ground for disease. There are two basic concepts to having a dry area, keep the water out to start with or dry it out if it gets wet. Locate them in high spots or where the water drains away from. Don’t put them in a low spot that collects water. Slope roofs or use gutters and downspouts so water runs away from the coop and run, not into them. Maybe use swells or berms to divert runoff away from them. Some of that depends on the lay of the land. Don’t use waterers that wet the ground.
When the weather sets in wet it can be really difficult to keep water out. One way to get the coop or run dry is to position them so the water has some place to drain to. It helps if you have a sandy soil instead of a clay soil also but unless you haul in a lot of sand that will depend on luck. Lots of ventilation will allow them to dry out also.
If I were building a coop in your climate, I’d go open air. Lots of ventilation. Cover it with a roof to protect from rain falling straight down into it. Have some overhang on that roof but make one wall out of wire to get maximum ventilation. On one end, hopefully the end that the worst of the wind and rain normally comes from, create a protected dry area for the roosts. Make the coop fairly tall so you can walk in there and block off that end and a small portion of the two side walls to create a rain/wind protected area. Take that wall all the way to the ground but leave the top open above the roosts for extra ventilation. Feed and nests need to be dry but positioned so the chickens don’t poop in them from the roosts. With the tops of those three walls open and the one wall totally open the coop will get good ventilation and your chickens will be protected from windstorms.
They also need shade. They need to be able to get out of the sun. That’s another reason for the roof, but sunlight does not always come straight down. They need some walls on the side to give them good shade.
I’d make the floor out of dirt. If you use bedding rain will blow in and wet it and bedding will hold that moisture. With good ventilation it will dry out even if it is made of bedding, and it helps to rake the floor or scatter some food treats on it so the chickens will rake it for you with their scratching, but a dirt floor, hopefully a sandy floor, will dry out fairly fast. Just make sure the water has some place to drain to instead of collecting in a low spot.
How much space do you need? You can follow the link in my signature to get my thoughts but the four square feet per hen in the coop plus ten in the run should fit your situation fairly well. The tighter I crowd them the more behavioral problems you ae likely to see, the less flexibility you have in dealing with problems, and the harder you have to work so I believe in providing plenty of room, but room can get expensive. Here, most building materials come in 4 foot or 8 foot dimensions. You can usually build a coop with these dimensions for no more expense and with less cutting and waste if you plan around the dimensions of your materials.
If you build an elevated coop with the floor up off the ground, you can use a wire floor. That would help with ventilation and would keep the floor dry, but you need access to clean the pop out from under that wire. Also chicken poop can be fairly large and a consistency that it will not go through the wire. You’d need some fairly large holes in that wire so the poop goes on through. Also not all wire is created equal. Some wire has sharp points at the welds or if it is galvanized, from the galvanizing. Those sharp points can be hard on a chicken’s feet. If you can find plastic coated wire of the right size you can avoid that problem.
I don’t like to put wire under a coop or run on the ground. It can be hard on their feet when they scratch, plus it tends to rust when scratched. To protect against digging predators, I suggest you use and apron. Take a 45 cm strip of wire and lay it flat on the ground outside your coop or run. Attach it to the bottom of the coop or run. Depending on the wire you can use J-clips, hog rings, or just tie it with wire. You don’t have to bury it but if you remove about 2” of sod and bury it that deep by putting the sod back on top, it is held down and is out of the way of lawn mowers and wed eaters.
For your research go to the Learning Center at the top of this page. There are all kinds of articles in there that can help plus many coop designs. There are several threads at the top of this section (the stickies) that can help.
https://www.backyardchickens.com/f/9/coop-run-design-construction-maintenance
I also suggest you read this article. The best time to fix a muddy run is when you are designing it.
Pat’s Big Ol' Mud Page (fixing muddy runs):
https://www.backyardchickens.com/web/viewblog.php?id=1642-fix-a-muddy-run
You are polite, asking if you can quote people. You certainly have my permission plus I don’t see any problems quoting any of the articles here as long as you properly bookmark them. This is a public forum and Nifty, the owner, likes all the publicity he can get.