Quick example of adding a meta box to WordPress based on user permissions

permissions-metabox.php

<?php
	// This is the important part. You only add the meta box if the user has the required capability(ies).
	// http://codex.wordpress.org/Roles_and_Capabilities
	//
	// You could add additional checks to ensure the meta box is only displayed on certain pages.
	if( current_user_can('my_custom_capability') ) { //Change the capability depending on your user permissions
		add_action('add_meta_boxes_page', 'my_callback_function');
	}
	
	/**
	* My Callback Function
	* Adds the custom meta box to the admin in the specified area.
	*
	* @return void
	*/
	function my_callback_function() {
		add_meta_box('htmlid', 'My Meta Box', 'my_metabox_callback_function');
	}
	
	/**
	* My Metabox Callback Function
	* Displays the meta box when called
	*
	* @param obj $post The current post (page) object
	* @return void
	*/
	function my_metabox_callback_function($post) {
		
		//Echo out your custom fields here. Instructions for saving your meta box on submit are here:
		//http://codex.wordpress.org/Function_Reference/add_meta_box
		
	}
?>