Hello! I am so jealous \:0) but really happy for you that you are getting a building for your girls. I have been trying to get my coop built for about a year now....almost there. Guess it isn't a priority yet... Well, my first suggestion was going to be to grab a nice tall ice tea, long island ice tea, or margarita. Sit down with some construction paper and scissors. I am not sure how well this might work for this situation, but, in my MANY, MANY office moves and our upcoming "remodel" I guess you can call it of our farm/ranch area around the house...moving livestock pens, re-doing water lines, etc., this is what I am doing...
Since you know the amount of space you are working with, and you know the number of things you want to put in there, you probably already know, even if you really don't know it (sorry, trying to be funny) how big some things should be. This would be, how long the roosting bars should be, how long this or that should be, how many rows of laying boxes, etc.
You will be cutting out the size (working on a 1" scale) of things. For example, Your shed will be 5' X 8', your base of drawing will be 5" x 8".
The items you cut out will help you place them onto the shed cut-out, move them around... It would give you a bird's eye view of the final... I know this sounds kinda crazy, maybe silly, maybe this isn't what you were looking for, but I hope it helps. I have saved myself lots of extra effort by using this type of planning.
If you do this, then imagine when you walk in, then on the right, what you will see, then imagine yourself doing your chores, your chicken's behavior, then how it opens up to your yard, etc... it may help you to be more creative in itself.
One thing I agree with you on. The poop board. People are so clever about this, but The best ones I have ever seen are those that slide in like a tray into an oven, then you just pull it out, dump it off, or spray down with the hose, then slide it back in. This way, evey your children or grandchildren might not be opposed.... just an idea.
Since my coop is going to be very large, I am hoping to do the same thing, but mine will be several of those pull out boards in a row, maybe 2' wide each.
Good luck.