Yep, with out those two walls - what seems easy just isn't.
If you have scrap wood -- you may be able to do one that is free-standing. with a strong enough base -- it would be pretty stable, and --- maybe you could get one that fits into the coop - and you could remove it whenever you need to clean out - because it isn't attached.
The 45-degree cuts on the base pieces are just for looks -- it could be done with just square-cornered pieces of 2x4.
If you have scrap wood -- you may be able to do one that is free-standing. with a strong enough base -- it would be pretty stable, and --- maybe you could get one that fits into the coop - and you could remove it whenever you need to clean out - because it isn't attached.
The 45-degree cuts on the base pieces are just for looks -- it could be done with just square-cornered pieces of 2x4.