If I understand your question, you want to design (or redesign) their site without others being able to see it... right?

If that's true, there are a few different ways. Your home page is typically index.html. If you place a default.html page online along with the site, visitors will see it rather than the index (it works alphabetically). So, put your coming soon page as the default and your home as index and you can work on it without people seeing it.

Another way is to design it in Wordpress. There's a plugin that creates a coming soon page when active. The only one(s) who can actually see the site is someone who is also logged into the dashboard.

Hope this helps.

Before I give you the right advice we need to know some things.

Is this a new site or redesign.

Is it on their hosting or your hosting

Usually when doing a site for a customer we transfer their hosting and domain to us.

Before finalizing the nameservers we set their domain on our servers and then we can work on it through the temp site.

http://myhosting.com/~username

Quentin

Well no one is really going to see it but if you want to hide it use this plugin.

WordPress › underConstruction « WordPress Plugins

Quentin

I use this one: WordPress › Custom Coming Soon Page « WordPress Plugins. I can make it look like I want.

If I'm redesigning a site they already have online, I build it on a temp site too (like Quentin said above) only I have a site that I bought years ago that I use for that purpose with do not index tags. It's a .info which only costs $1.99 year and is generic named so I can use it for different customers (or, if the customer is big enough, I get an info for one of their keywords and give it to them when I'm done with it as a bonus. I don't tell them that it's theirs until I get done and they're always impressed since they don't know the cost).

Once the site is complete and ready to transfer, with Wordpress, it's simple to move. Wordpress.org has a small write-up telling you exactly how. There's reports you can buy to do this too but why buy something that is easy and free?

What you want to do is develop it on your local server, then when it is finished, transfer the files to the hosting, copy out the database and import it to the hosting, change the config files with your live database details and go live.

I use WAMP server, google it. You just dowload and install it, and you have your localhost server set up.

Google "wordpress transfer from localhost to server" for a big list of tutorials on how to transfer from your local server to your live server.