It's amazing how many things you can build simply using PVC pipe. If you ever enjoyed lego sets, you will have fun putting together all sorts of constructs with PVC. Because it is a cheap material, you can create all sorts of frameworks for less than wood or metal. It is easy to cut, looks clean and white and is remarkably light.
Although PVC pipes and fittings are primarily used for irrigation systems for the garden, these materials lend themselves to construction. You can build useful toys for children, frames for holding things, bases for crafts and all kinds of structures with PVC.
You can find elbows, tees, and multiple angle connectors to build whatever shapes and angles you want. Essentially, you are creating a framework. PVC pipes and connectors can be used to build light shelving, underwater tables to support bog plants in ponds (allow the pipes to fill with water to discourage floating), dog jumps for training, small shade kennels for pets, easels for showing art work -- even frameworks to store other pieces of pipe upright in the garage. The possibilities are limited only by your imagination. You simply slot PVC pipe into different connectors and build whatever shape you want.
Cover the PVC framework with paper, cardboard, screening or cloth, depending on how you want to use it. Make your structure something that will float in water by sealing the ends with caps. You can even paint the PVC.
Be aware that although PVC is quite strong, it will snap or break with a lot of pressure. Stabilize your structures by using PVC glue to solidify all joints. PVC is has an advantage over wood and metal by being so light but it has less tensile strength. PVC is not good for building serious weight-bearing structures -- especially for human weight.