Geweb

Use this plugin if you want allow users create their own sites based on your.
<h3>Arbitrary section</h3>
You can create your own HTML code of the form. 
Create file in your theme, put code from plugins/wp-auto-mu/geweb-mu/register.php to your new file and add_filter geweb-mu-register-path to rewrite file paht for the form.

WPMU User own site

Plugin allows to create site on user registration in WPMU environment.

Kezz Bracey

s2Member Buttons is a helpful tool for users the s2Member plugin, an awesome free membership site system by the folks over at WebSharks / Primo Themes.
Once installed, s2Member adds twelve extra buttons to your post editing toolbar.
These buttons can be used to easily add shortcodes into your content that control display for users with various access levels.
There is also an extra function to display a user’s EOT (end of term).
And there is the ability to output a list of all sites a member can access in a multisite network.
The twelve buttons, in order, are:
<ul>
<li>List member’s sites – for multisite networks</li>
<li>Show member EOT</li>
<li>If logged in</li>
<li>If not logged in</li>
<li>If level 1 or above</li>
<li>If not level 1 or above</li>
<li>If level 1</li>
<li>If level 2</li>
<li>If level 3</li>
<li>If level 4</li>
<li>If level 0</li>
<li>Public</li>
</ul>
These buttons have been really handy for me, so here they are for any other s2Member users who’d like to have them as well.

s2Member Buttons

Add buttons to your toolbar that help you control content presentation in an s2Member based membership site.

WPMU User own site vs s2Member Buttons