I bought my coop from an Amish man who built coops and the design was already created. I added a large dog cage tray under the roosting bars to collect the majority of the poo. The tray fits the area perfectly so it works for me. I also use the deep litter method - adding PDZ and diatomaceous earth as supplements to the coop to control parasites and ammonia buildup. The only area poo accumulates - other than the bottom tray is a small amount along the edge of the wall at the top of roosting bars from the chickens on the top rung of the bar. I clean this area weekly scraping the poo down onto the tray below.
See photo attached: Poo tray under roosting bars