By using old pallets and 55 gallon plastic drums, these guys built a transportable pontoon raft. This pontoon raft is really nice if you have a river or lake next to your house. It is a great way to cool down and have fun in summer. Check out how it is done in the following link.
Alternatively you can use PVC pipes to float the pontoon raft. Watch how it is done by Ray Pena. He even powered it up with a motor.