I'll post a couple of photos to see if it helps you. My coop is a lot bigger than yours but maybe it will help.
The first one shows my main roosts over a built-in brooder. It doesn't look like it but the brooder is 3 feet wide, the first roost is about 12" off the wall and the other roost is another 12" over. The brooder did not go the entire length so I put bins underneath the open area to catch the poop.
View attachment 2190738
This one may be of more interest to you and shows you some things to not do. This is my juvenile roost, in here to give a place for my juveniles to sleep that is not the main roosts and not in my nests. The nests are 16" deep and the roost is probably 8" of the wall. It works for juveniles and would for bantams. The top two nests are late additions as is the roost. I use the nest tops as droppings boards so that should answer the question will they use nests under a droppings board. This one is a pain to scrape. If I had it to do again I'd put one board across the top so it would be easier to scrape.
View attachment 2190737
Mine have all kinds of clear landing space so I don't need ramps. That's one of the problems with smaller coops, not much room. Putting a 2' wide droppings board in a 4' wide coop doesn't leave much room for you to work in there.
I think those nests are on a long wall? I don't know how much roost space you actually need for five hens. I've seen all kinds of numbers given, 7" per bird all the way to 15" per bird are pretty common. I assume your hens are all full sized and not bantams? Are they extra large like Jersey Giants or Brahma's? For five full sized hens that are raised together I'd put the roost across the four feet wide end of the coop away from the door. From my experience that should be enough and it maximized the room you have to work in there. I consider your convenience and comfort a big part of coop design. You may not have enough room for a ramp
I don't know what your ventilation looks like. In summer in Montana they will enjoy a cool breeze from open windows. But in winter those windows need to be closed. They still need good ventilation. Hopefully you have some up high so breezes don't hit them.
I just put the nesting boxes in at 15” off the ground on the left wall
I assume this means the bottom of the nests are 15" off of the coop floor. How tall are those nests, maybe 12"? You want the roosts to be noticeably higher than anywhere you don't want them to roost, like the top of your nests. If you had a large coop and the roosts were across the coop on the far end I'd want maybe 12" minimum difference in elevation so they would notice. But you are not. If you look at my juvenile roost you can see how much higher they are. The bottoms are up just a couple of inches. That works to get them to sleep on the roosts. It does not give me enough room to scrape the poop under the roosts, another mistake I made so watch that.
I'd put the droppings board at the top level of the nests with the roost a bit above that. They will probably use the droppings board as a step to get to the roosts though mine often fly straight up 5' to the roosts. And mine usually fly back down from the roosts instead of hopping down on the brooder top. Yours might even use the nest tops as a step to get to the roosts. Unless you have some double extra huge breeds or some that can't fly like Silkies they should be able to get up and down without a ramp.
Another option. Put your droppings board at the level of the bottom of your nests, 15" up. They can use that as a step to get up to the roosts. The problem with this is that you want to feed and water under there and 15" doesn't give you much room. I don't know what your feeder and waterer will look like, maybe they will fit. Or maybe take the nest off the furthest from the roost and feed and water way over there so they don't poop in them from the roost. That might give you better access to them anyway, depending on where your people door is and if your door swings in or out.
It's been enjoyable overthinking this with you. Good luck!