I used 3/4 thick PVC pipes, three 90• elbow fittings and one hose to PVC pipe fitting. I drilled holes through the top of the structure, spacing them out about 3" wide. The kids love running through the structure but also love trying to escape the water by going between the streams (the drill spacing). I used PVC cement (glue) to hold the pipes together.
Total cost is less than $10!