Welcome to BYC. Where, in general, are you located? Climate matters, especially for housing.
If I counted right, you're planning on housing 18 chickens, yes?
The Usual Guidelines
For each adult, standard-sized hen you need:
- 4 square feet in the coop (.37 square meters)
- 10 square feet in the run (.93 square meters),
- 1 linear foot of roost (.3 meters),
- 1/4 of a nest box,
- And 1 square foot (.09) of permanent, 24/7/365 ventilation, preferably located over the birds' heads when they're sitting on the roost.
So, you will need at least:
- 72 square feet in the coop -- Technically that's 8x9, but given the common dimensions of lumber and other building materials you might find it easier to go up to 8x12. Extra space is always good and you can use some of it for storage.
- 180 square feet in the run
- 18 linear feet of roost
- 5 nest boxes
- And 18 square feet of permanent, 24/7/365 ventilation.
What are the dimensions of the existing facilities? I wonder if you could achieve the necessary square footage by attaching the red coop to the coop/run with the chainlink, and adding the necessary walls for your climate to make the entire thing into a coop then just have the new, 180+ square foot run to build?