The rubber is fine for chickens.
You might want to look into using these mats, Flexgard Multi-Use Utility Mat. They are available at TSC and come in different sizes. They are 1/4 inch thick, you could do it in one piece and would be more economical. I used a few of these to put down in the goat stall, then put shavings on top. The chicken coop is a barn stall dirt floor, doing deep litter method there.
You might want to look into using these mats, Flexgard Multi-Use Utility Mat. They are available at TSC and come in different sizes. They are 1/4 inch thick, you could do it in one piece and would be more economical. I used a few of these to put down in the goat stall, then put shavings on top. The chicken coop is a barn stall dirt floor, doing deep litter method there.