What are your ideas for transforming this dog run into a chicken run?

So I moved into a great old house that comes with an old dog run (/tree fort!) that I would like to turn into a chicken run. It's got four chain-link walls, a cement floor with drain, and a tiled roof; but is by no means predator-proof yet. I would like to cover the floor with pea gravel (which is readily available from an area that is going to be repurposed for garden planters), install natural brances for run perches, and I have some ideas for predator-proofing it, but I'd like to hear what the BYC experts would do with this space. All the materials need to be reclaimed/low-cost.

Please lend me your ideas!

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