I've seen large-scale xylophones similar to this one at a couple of kid venues, and funnily, despite my stated penchant for large, noise-making doodads, it's never occurred to me to try to build one. That is, until this Instructables how-to came along.
Says Instructables member dirtydiaperchanger, who guesstimated these plans after seeing a similar xylophone at a children's museum: "This project consists of three 2x4x8' kiln-dried lengths of lumber (don't use pressure treated... bad for kids), about 15 feet of rope, some staples and a wooden dowel. The total cost is under $10 and it can be made start to finish, including clean up, in about an hour. I made this for free from scraps I had on hand."
See the detailed tutorial here.
Images: Instructables member dirtydiaperchanger