I'll try to help as well. In Lord of the Flies, Piggy was an intelligent yet physically weak boy who was teased and mistreated for being different than the other boys. His death at the hands of Roger was particularly tragic because it symbolized the death of reason.
As you write your elegy for Piggy, reflect on his characteristics which are most noteworthy or honorable. Metaphors are like symbols, so consider including symbols from your class discussions or items in the book that were connected with Piggy.
As for a rhyme scheme, it seems like you get to choose whatever pattern you like. Just make sure it is consistent. For instance, if you rhyme the second and fourth lines of one stanza, make sure you do the same in the second stanza.