hala najmood.. well it depends what do you exactly mean by building vocabulary.. is it for the SAT??? or do you just want to improve your skills in building vocabulary?? I suggest you visiting these websites that will help you learn more about how to improve your skills in building vocabulary:

uic.edu/depts/counselctr/ace/vocabulary.htm

you may also need to have a look at this website because it has good links to other webpages. But the focus here is on latin and greek words because many english words were derived from those languages:

wordfocus.com/

Cheers