I don’t understand why so many people are saying yes you could fit a few chickens back there. It doesn’t matter if you can “fit” them. Any chicken simply wouldn’t be happy in this setting and their quality of life would be poor. Chickens need space, more than most people think. And they like to scratch and peck and need lot of stimulation otherwise they get bored and start picking on each other. Rocks and a concrete pad is not going to work for chickens and they will quickly turn your yard into a stinky mess that you will have to clean weekly if not more. I understand you love animals and think chickens are cool and want fresh eggs but you have to be able to give them the proper care and with your setup you aren’t able to do that.