here's mine: http://twitya.com/503.php
The .htaccess is as follows:
Options +FollowSymLinks
RewriteEngine On
RewriteBase /
RewriteCond %{REMOTE_ADDR} !^12\.345\.678\.901
RewriteCond %{REQUEST_URI} !^/503.php [NC]
RewriteRule .* /503.php [L]
[the ip address is my own so I can access the site]
top of 503.php:
header("HTTP/1.1 503 Service Temporarily Unavailable");
header("Status: 503 Service Temporarily Unavailable");
header("Retry-After: 86400");