How long would you estimate that I have until they will be ready to be outside?
I do have a backup plan for if the coop isn't ready in time, an existing space that I could enclose and use.
Like Quinstar says, about 6-8 weeks, after they are fully feathered.. It is summer, so that should be fine. However, now it is 5-7 weeks, since you already have them coming and they are hatched?
Our first night, the temp dropped to about 40 degrees. We worried, but also had a very secure heat lamp in the coop. They survived just fine.
Building a coop is like retirement, the time to start saving/planning is yesterday.