Here is my coop. It's a lot like what you are building I think. The "hen house" itself is 4'x4' square. The Coop (Dog Kennel) is 12'x12'. The covered ramp and Pullet Shut Auto door were just added in the last couple of days. For the past 4 years I've just had a scrap sheet of wood for a ramp up to the main door there in the front. I just kept it open all day. You can see it outlined by trim on two sides in this photo. We had a raccoon problem and I got tired of opening and closing the door every day (not to mention trying to leave town even for a night was a joke) so I installed the auto door.
Don't get me wrong, I'd love to have some of the amazing coops on BYC but for me it's not a reality. This humble little coop has served me and my birds well. I have 13 birds crammed in here. It works though because they only go in the house to sleep or lay eggs. Food and water are outside. They also get free run of my backyard most of the days. I do have to clean my coop quite often. For roosts I used 2x4s. There is one the full length of the coop along the side where the auto door is now. They have to go under the roost to go in and out that door. Hasn't been a problem. Along the opposite side of the coop is a roost of the same making that goes 1/2 the length of the coop. There are 2 nest boxes that take up the rest of that side. I have a 4"x12" vent cut in the back that is covered with a screened vent cover and then there are two 1" holes drilled in the main front door for cross ventilation. I haven't had any problems or bird loss with this coop and it was made with mostly scrap materials.
One suggestion I might make is to set your coop up on cinder blocks. You can see in the bottom corner of my coop there is a cinder block with a bracket for a 4x4 post supporting my coop. This serves two purposes, one being it gets the coop a little higher off the ground (my chickens love to hang out underneath in the shade or when it's raining), and two it saves your posts from rotting. Just a thought
Don't get me wrong, I'd love to have some of the amazing coops on BYC but for me it's not a reality. This humble little coop has served me and my birds well. I have 13 birds crammed in here. It works though because they only go in the house to sleep or lay eggs. Food and water are outside. They also get free run of my backyard most of the days. I do have to clean my coop quite often. For roosts I used 2x4s. There is one the full length of the coop along the side where the auto door is now. They have to go under the roost to go in and out that door. Hasn't been a problem. Along the opposite side of the coop is a roost of the same making that goes 1/2 the length of the coop. There are 2 nest boxes that take up the rest of that side. I have a 4"x12" vent cut in the back that is covered with a screened vent cover and then there are two 1" holes drilled in the main front door for cross ventilation. I haven't had any problems or bird loss with this coop and it was made with mostly scrap materials.
One suggestion I might make is to set your coop up on cinder blocks. You can see in the bottom corner of my coop there is a cinder block with a bracket for a 4x4 post supporting my coop. This serves two purposes, one being it gets the coop a little higher off the ground (my chickens love to hang out underneath in the shade or when it's raining), and two it saves your posts from rotting. Just a thought