The biography should be 3-4 pages or about 1000-1250 words. The biography should be in a narrative format with an intro, body, and conclusion, rather than an interview format (Q & A).
This biography of Sonia Sotomayor is a good example of a format for this short biography.
http://www.biography.com/people/sonia-sotomayor-453906
Here’s a biography of Junot Diaz that is in a journalistic style, that also incorporates his work and voice. It weaves the biographical information between mention of events (Pulitzer prize) and quotes (from fans and by Diaz).
http://www.cbsnews.com/news/the-wondrous-life-of-junot-diaz/
You will want to start with an overview which can be some basic biographical information or a sentence or two that foreshadows themes that you will cover in the biography. Then, you should find an interesting way to divide the narrative into specific parts that are relevant to the topic of immigration. You should conclude with a brief statement that summarizes well the theme covered in the biography.