How can I let users open the site for other visitors?

Question

I'm a bit new to wordpress and php and I'm trying to create a site where users have the possibility to change the appearance of the index page for other visitors. This could perhaps be done with back-end access to a maintenance plugin but I want it to be more simple than that for the user. Basically just log in and then push a button to open the site.

What would be the best way to achieve this?

---

[Update]

# Plugin name 'Name' => 'Maintenance Mode',
# Author of the plugin 'Author' => 'Michael Wöhrer',
# Authot URI 'AuthorURI' => 'http://sw-guide.de/',
# Plugin URI 'PluginURI' => 'http://sw-guide.de/wordpress/plugins/maintenance-mode/',
# Support URI: E.g. WP or plugin forum, wordpress.org tags, etc. 'SupportURI' => 'http://wordpress.org/tags/maintenance-mode',
# Name of the options for the options database table 'OptionName' => 'plugin_maintenance-mode',

Answer 1

Based on Bainternet's answer to this question:
Save Theme Options (options.php) From The Frontend

The key is to know the name of the plugin option to Enable/Disable the Maintenance Mode.
In this example, it's named: my_maintenance_mode

<?php 
    if ( isset($_POST['mmode']) && isset($_POST['action']) && $_POST['action'] == "update_mmode" ) {
        if ( wp_verify_nonce( $_POST['theme_front_end'], 'update-options' ) ) { 
            update_option( 'my_maintenance_mode', $_POST['mmode'] );
        } else {
        ?>
            <div class="error"><?php echo 'update failed'; ?></div>
        <?php
        }
    }

    // DISPLAY FORM ONLY FOR THESE ROLES
    if( current_user_can( 'administrator' ) || current_user_can( 'editor' ) ) {
?>

<form id="save-mmode" name="save-mmode" action="" method="post">
<select name="mmode">
<?php $selected = get_option('my_maintenance_mode');
    <option>Enable/Disable Maintenance Mode</option>
    <option value="1" <?php if ( $selected == 1 ) echo 'selected="selected"'; ?>>Enabled</option>
    <option value="2" <?php if ( $selected == 2 ) echo 'selected="selected"'; ?>>Disabled</option>
</select>
<?php wp_nonce_field( 'update-options', 'theme_front_end' ); ?>
<input type="hidden" name="action" value="update_mmode">
<input type="submit" name="update-options" value="Save">
</form>

<?php
    } // END if(current_user_can)
?>