I'm really lucky that I have 2 HUGE sheds which where already built when I bought my house. The one I use for the chickens is about 360 square feet, so for me the space is fantastic.
I recently gave them a kitchen table with some roosts attached to the top. I have some plastic poop boards that sit on the table top. Since the poop boards it's cut my cleaning time, and the amount of bedding I use drastically. I used to clean them out every two weeks or so, it took me an hour or so. I also used about three bales of straw each time. Now I clean the boards every other day, and sprinkle a little shavings on them. I've not had to clean the coop out since the boards where put in, about 5 weeks or so.
And lastly it's secure. I've not had any problems with night time predators for the two years that they've been in there.
SO:
1 space
2 poop boards
3 secure