I'd cover that metal floor with some vinyl, or even cardboard, then some pine shaving bedding.
The slide out aspect will probably not function with adequate bedding.
The heavy winter coat worn inside a heated house is a perfect analogy, one that is hard to misinterpret as everyone had probably experienced it. Yes, they are ready to go outside.
Ditto the ventilation observations...I'd also beef up the size of that roost, go to at least 2x2, better yet a 2x4...