The playset part has a lot of advantages, has plastic windows, doors, etc (it was one of those huge Costco ones)
This coop page about converting a Rubbermaid shed will probably be helpful to you in working with the plastic:
https://www.backyardchickens.com/articles/the-scoop-on-a-rubbermaid-big-max-coop.76444/
We're going to pick 10-12 favorites
Here's the math worked out for you:
12 hens
- 48 square feet in the coop. 6'x8' is more practical than 4'x12' since a long, skinny coop like that would be difficult to work inside.
- 12 feet of roost
- 120 square feet in the run. 10'x12' or 8'x15' -- 8'x16' means fewer odd cuts than either of those. 6'x20' is possible, especially if your run is an open-topped, fenced area instead of fully-enclosed with a solid and/or wire roof but risks social problems because subordinate hens need to be able to pass the dominant hens at a respectful distance.
- 12 square feet of ventilation.
- 3 nest boxes.