Here is a materials list for building a hollow wood paddleboard. I usually buy 5 rough sawn 2" x 6" boards that are at least 4" longer than the boards length. This yields more wood than you need but ascetically it is nice to have some wiggle room. If you buy boards that are more than a foot longer than you need you can cut off excess as your solid blocking before you mill it into 1/4" strips and planks.
Glass & Glue