WHAT BUILDING MATERIAL SHOULD BE USED FOR MY PROJECT?

Pressured-treated lumber (PT) works for dock and raft construction. It is the cheapest material available and weathers well (all cut ends must be treated with preservative).

Cedar possesses natural rot-resistance, and typically outlasts PT. It is, however, about twice the price. To cut costs, you could build the substructure from PT and deck the swim raft with cedar.

Composite materials – a combination of wood and plastic (some are 100% plastic) – can be used for the swim raft deck, but lack the strength needed for the substructure. They also look good, and are an environmentally friendly recycled product, but composites are two to four times as expensive as PT.