I didn't build a playground per say, but I did create a rooftop playground on top of their cage. That's where they get their out of cage time. (I've been neglecting out of cage play this week because my mom has been sick and needs continuous care since coming home from hospital. When in hospital I spent my time being all over the place between there and work).
Anyway, I used the top of cage to store some of their accessories, they always wanted to go up there during out of cage play, so I decided to reorganize it. I set it up so they can play up there. Since photo bucket got stingy on sharing, I don't do to much photo posting on the forums. I did make YouTube vids on some of my cage designs (setups), including the rooftop playground. If you wanted to have a look, search for Terry Jones on YouTube.