If you are working on a book, don't wait until its finished to build your web site. Once your book launches, you'll find yourself busy with hundreds of other things, and a publicity campaign is much easier if the web site is already in place.
As I've helped people with this task, I've noticed they gain clarity about the book, and about how to focus or pitch the book by having a web site. It forces you to make a nice, concise statement about the book, to capture attention. And that will later become the theme for your entire book campaign.
So don't wait - choose a domain name for yourself or the book's title, as I did with Release Your Writing (www.releaseyourwriting.com) and begin letting your site reveal the focus of your book. You'll also have a place there to list upcoming events and let people know how to purchase, but you might enjoy it as a visual representation of what you know is soon to come: your book.