From "pen" to "habitat"

[RTA1197]

We have had 2 Pekin drakes and 1 Swedish hen for the last year in a 10' x 20' pen. A few months ago, we got 4 more Swedish hens.
We don't like the pen that we have them in, we feel like it could be a lot better. It's not very good when the temperature gets up into the hundreds and it's kinda high maintenance. We are going to about triple the size of the pen which will allow us to have a bigger pond (the drakes run the new ones out of the kiddie pool), have to permanent vegetation for quality shade and possibly as a extra food source.
So, one of my questions is, what would be good choices for vegetation? Maybe the shorter list would be what to avoid. We have learned that nightshades are a no-go. But what kind of perennial clump grasses? What kind of shrubs would be okay? Rose bushes maybe?

 

[Nats Chickens]

Roses and herbs.

 

[Miss Lydia]

Nothing with thorns inside their pen or you'll be dealing with bumble foot. Growing climbing roses on the outside and over for sun protection would be a good idea.