I agree with Mario, though I've never done a science fair project in my life so I only have an idea what it's about from television and movies. But he's right concerning the difficulty it would be with getting data from lucid dreamers, especially new ones or non-naturals. Did your teacher give you any advice? Are you a natural lucid dreamer? Or just interested in the subject? How familiar are you with lucid dreaming? One of the problems with doing dreaming as a topic for a science fair is that all of the information will be entirely subjective and any data anecdotal at best. Like I said, I'm not familiar with science fairs or how they are judged, but I would assume you would need a more solid and objective sort of topic. I could be entirely wrong on that though. You should probably discuss it more with your teacher.