Actually, if you are genuinely serious about getting something published, such as in a book, be very wary of posting it online. Granted, this is not firsthand knowledge on my part, but by "publishing" online, a friend of mine was unable to secure a traditional paper-bound publisher for that reason regarding a story, having already put it up online.
Without researching or consulting an expert, I'm not sure if that's a problem with all websites, ie. any sort of prior publication, or if that's just an issue with certain websites, but if you actually have something that stands a chance of publication, I'd go carefully just in case. It's hard enough getting published without adding extra hurdles.
That being said, I highly doubt the odds of getting anything based off of official LEGO themes published is likely at all--unless you somehow managed to publish it under their auspices, so I wouldn't worry about that... a slick website is probably the best publication you can hope for.