US1M constrution question 2 "booms"


Was reading threw the US1M construction manual again. Ok fine it is about the 100th time.

on page 41 Booms
What material works best for jib boom and main sail boom??
Also why is the jib boom and main boom shaped like they are? Is there patterns online for making them or is it builder choice on how to do it???

The only thing I know is that they must fit through a 3/4" radius hole.