I gonna stick my nose in this only because I own a commercial concrete
company. Here is the skinny on concrete. That rough finish is called a
broom finish. It can be a fine broom or a medium or rough finish depending
on how long you wait to broom it. Its rough because you won't slip on it.
The best finish for a chicken coop floor is hand trowel finish. No broom
with a steel trowel finish thats not slick but its not rough either. Its
allows you to hose it off with a garden hose and also somewhat water
proofs the concrete by fusing the top layer together. Its more sanitary
and the finish of choice with the droppings of animals and urine. It can be pressure washed with high pressure water or boiling water for that matter with no damage to the finish. Shovels and pitchforks will slide right on the
top without gouging the finish. Its hard with resiliency. If you can slope it or have a rise in the middle it will help with the run off.
If you can afford to hire someone to do it for you it will be much easier.
Ride a construction area or a neighborhood thats under construction
and look for a group pouring a driveway or patio or house slab. Chances
are they may have some concrete left or will order you some at their
price and every finisher I've ever known like to make a few extra bucks
on the side. Its worth it to check it out.
Avoid the concrete in the bag, you can't mix it bag after bag in a consistent manner to get it to hold up. Water is the enemy of concrete.
Too much water weakens it.
A good finish is no accident. If you don't have the tools and a basic
understanding of the product, its not gonna last and not going to be
functional.
We have a saying: Every homeowner is a concrete finisher till the
truck shows up. Its funny but true. Make sure you leave a gap around
the bottom of the coop so you can wash out the droppings.
Thats my 2 cents.
By the way, my company bought, placed and finished 11,265 yards of concrete last year and I've been in that business 30 years.
jim