I would take this and adjust the height for a slide, include more of an angle on the ladder for my younger son and put a beam out the side for a swing .and maybe a sandbox underneath instead of a solid floor?
Love my rain barrels may get more! Really great idea for saving water! Rain water is better to water flower beds with, so this is an awesome idea. I saw this on a show not too long ago. You can hook up your hose and water your garden too.