Playviaries?

I'd like to rig up something so the birds could have an outside, enclosed playpen-like area to be outside with us for sun and fresh air, a bit more entertaining than a small "hotel" cage. It would also need a fairly secure way to transfer the bird inside from a carrier. I don't think we could afford multiples, so it would need to accommodate small to medium birds.

This is probably more of a longer term project than an immediate purchase. I know you can buy walk-in aviaries ready made but that seems a bit of overkill.

Any ideas?