You have a lot of good opportunities with that building. There is not a lot of overhang on the sides, so those covers/baffles Elmo has look like a great idea.
I put outside access to my nests and find I just don't use them. Some people do and love them, but I find it easier to just go inside and get the eggs. Besides, I like to look inside the coop to make sure everything is OK. I found a possum in there once. Another time, I found a dead chicken in there. Then there was the time the black snake was in there. A big black snake. I do like to look inside when I gather eggs.
Remember that space under the nest boxes is measured from the top of the bedding, not the coop floor. They will scratch a lot and maybe raise the level of bedding to where it is not useable. A nice dark cozy place under there might look like a good place to lay eggs. And if it is not accessable to chickens, it makes a great safe place for Mommy Mouse to raise her young.
As great as that poop board design looks, with your number of chickens, you might want to consider if it is the right design for you. I agree you need plenty of space on the roosts. It is not that they take up a lot of space once they are up there. They don't. They like to snuggle up with their buddies and really don't take up much room when they are up there. But they spread their wings when getting up there and need space for that. They also move around a lot sorting out who gets to sleep nest to whom. That takes space. I also find that my chickens are really vicious enforcing their pecking order rights when on the roosts. The ones lower in the pecking order need room to get away from the ones higher up.
I also have a dirt floor with aprons around to stop digging predators. If you do elevate it, you will either have to get under there at some point (chickens laying under there, sick or injured chickens, something) or if access is denied, it is a great place for Mommy Mouse, Mommy Rat, a snake, something, to set up residence. If you elevate it, I suggest you elevate it enough.