[quad]

For the high goal we used:
about 75% of one sheet of 1/2 ply
about 85% of one sheet of 3/4 ply
4 2x4x10
4 2x4x8

For the low goal:
most of one sheet of 3/4 ply

This assumes you are following the plans as presented.

You can use a free cutlist program to give you a cutting diagram.

The high goal is top heavy; consider some additional supports/anchors.