One of my play pens is built almost identically, you'll love it.
I would suggest you think about using a silicon sealant on the bottom of the exterior walls between the steel sheets and the concrete base. I had ingress of fine dust and insects, including ants who thought they were in heaven. Also repels ingress of water when it buckets down, as it does every now and then. This happened even though the inner walls were lined to the floor and sealed.
Mick.
I would suggest you think about using a silicon sealant on the bottom of the exterior walls between the steel sheets and the concrete base. I had ingress of fine dust and insects, including ants who thought they were in heaven. Also repels ingress of water when it buckets down, as it does every now and then. This happened even though the inner walls were lined to the floor and sealed.
Mick.