Since it is your task to actually write, the editors at enotes do, indeed, provide suggestions and ideas. With these suggestions, you, then, should be able to compose your lines.
Regarding the figures of speech, you can use Piggy's glasses to represent him; that is, use synedoche. e.g. It was the glasses [meaning Piggy] that taught us all to reason
In order to write a metaphor, return to the various descriptions of Piggy; in the beginning his physical description includes his myopia, his rounded body, his thin hair--he is much more like an older man than a boy. Draw upon his likeness to an older man to make the unstated comparison of a metaphor.
Also, for ideas on how to compose this elegy, why not look up elegy so that you understand the tone and form, and read some elegies that have been written by famous poets? By doing so, you will understand the form and rhyme of an elegy, which originated with the Greeks. Among the famous poets who composed elegies are Edmund Spenser, John Milton, Thomas Gray, Percy Byssche Shellye, William Cullen Bryant, Alfred Lord Tennyson, Walt Whitman, William Butler Yeats, and Ben Johnson (who wrote "On My First Sonne" about his deceased child--an excellent example for your purposes: a melancholic poem that conveys the deep loss of the father).