How can I customize domain in url

Yes, you can surely make it happen. User 1 will navigate to user1domain.com and the next will use their own userxdomain.com (where x is the ID of the user), but only if you are willing to buy the domain name for $10+ per year. And according to me, this would be the worst way to start your business or application.

http://shop.domain.com/domains/[^]

What I would recommend is to use something like this, user1.domain.com and then provide a different URL for other users, like user2.domain.com. Many services are already using this mechanism, Tumblr, Wordpress, Blogger and so on. This mechanism is known as using "sub-domains". You can access the sub-domain using PHP or any other server-side language, ASP.NET would also work!

http://serverfault.com/questions/63200/how-do-i-create-subdomain-names-dynamically[^]
http://stackoverflow.com/questions/13875273/dynamic-subdomain-with-htaccess-not-redirect[^]

Another way of doing the same is using the URLs, friendly URLs, and then providing the parameters to the URLs. Like, domain.com/session/user1. This is a very simple way of doing anything. You can create a page "session" and then fetch the parameter "user1" and load his content in it.

The methods that I have provided you with are free of cost. You can create 1000+ users and provide them a different layout, page and so on, without having to pay another fortune cookie at all.

Thank you, that is a good idea.. But I have read that there is another way without buying the domain name. ie adding code in web.config file.

<rules>
    <rule name="Rewrite subdomains">
        <match url="^/?$" />
        <conditions>
            <add input="{HTTP_HOST}" pattern="^(.+)\.foo\.com$" />
        </conditions>
        <action type="Rewrite" url="http://foo.com?barvalue={C:1}" />
    </rule>
</rules>