You could do this as a project (since it seems to interest you). But one thing you should consider is that as a "science" fair, your teacher and the judges are probably going to be looking for a project that has a hypothesis, control and experimental subjects, and/or dependent/independent variables. If so, just seeing what plants can be used or making fragrances yourself isn't going to fit the criteria they'll be looking for.
BUT, you could adapt this to make it work. You could make/buy essential oils from two different plants, and see which lasts (is detected by someone) the longest. Or, as strict "aromatherapy", you could develop a questionnaire to give to participants as a "before and after" introducing the scent. You could try a hypothesis such as "Does the fragrance produce a calming effect?" and ask participants to "circle a number" which represents their state of mind before and after the fragrance is introduced. Or "Which fragrance helps you to remember best?" and give the participants two different lists of thing to remember, one before and one after (the lists would have to be different so the participants didn't already know some of the items, but the items should have the same number of letters and be as common/unusual as those on the first list). To be absolutely fair, you might want to do your trials so that some people got to smell the fragrance first and some didn't, and a day later, switch them. That way, there wouldn't be any "aftereffects" if the fragrance helped them to memorize the lists (and maybe if there's any effect, you'll find something you can use to help you study for tests!).