Wordpress full-width post width get_post_meta() and 'add_meta_boxes'. Works with my css grid system. Screenshot : http://i.imgur.com/CgTaLuH.png

content-single-full.php

<?php while (have_posts()) : the_post(); ?>
<div class="main-content col-1-1">
    <article id="post-<?php the_ID(); ?>" <?php post_class(); ?>>
        Your single post content
    </article>
</div>
<?php endwhile; ?>

content-single.php

<?php while (have_posts()) : the_post(); ?>
<div class="main-content col-9-12">
    <article id="post-<?php the_ID(); ?>" <?php post_class(); ?>>
        Your single post content
    </article>
</div>
<?php get_sidebar(); ?>
<?php endwhile; ?>

function.php

/**
 * Let's build this fucking 'full-width' post feature.
 * It took me about 2 hours on stackoverflow to find a fucking solution.
 */

add_action( 'add_meta_boxes', 'wpsb_meta_box' );
function wpsb_meta_box() {
    add_meta_box( 'wpsb-meta-box', 'Full width post?', 'wpsb_meta_box_callback', 'post', 'normal', 'high' );
}

function wpsb_meta_box_callback( $post ) {
    $values = get_post_custom( $post->ID );
    $check = isset( $values['wpsb_meta_box_check'] ) ? esc_attr( $values['wpsb_meta_box_check'][0] ) : '';
    wp_nonce_field( 'wpsb_meta_box_nonce', 'meta_box_nonce' );
    ?>
    <p>Hide the fucking sidebar for this post?</p>

    <p>
        <input type="checkbox" name="wpsb_meta_box_check" id="wpsb_meta_box_check" <?php checked( $check, 'on' ); ?> />
        <label for="wpsb_meta_box_check">Full-width post pls!</label>
    </p>
    <?php
}

add_action( 'save_post', 'wpsb_meta_box_save' );
function wpsb_meta_box_save( $post_id ) {
    // Bail if we're doing an auto save (yep, i know, this is crappy)
    if( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) return;

    // If our nonce isn't there, or we can't verify it, bail
    if( !isset( $_POST['meta_box_nonce'] ) || !wp_verify_nonce( $_POST['meta_box_nonce'], 'wpsb_meta_box_nonce' ) ) return;

    // If our current user can't edit this post, bail
    if( !current_user_can( 'edit_post' ) ) return;

    /* Now we can actually save our checkbox.
     * In your database, the meta will be saved in the table 'wp_postmeta'.
     * You can see that the 'meta_value' for your 'post_id' is set to 'on' or 'off'.
    */
    $chk = ( isset( $_POST['wpsb_meta_box_check'] ) && $_POST['wpsb_meta_box_check'] ) ? 'on' : 'off';
    update_post_meta( $post_id, 'wpsb_meta_box_check', $chk );
}

single.php

<?php
/**
 * @package WPS-Blog
 * @since 1.0
 */
get_template_part('templates/header');
/* If the post has a meta_value set to 'on' in database,
 * it means the post is 'full width' so we need the sidebar (content-single.php)
 *
 * If the post don't have a meta_value set to 'on' in database,
 * it means the post is not full width so we don't need the sidebar (content-single-full.php)
*/
$key = get_post_meta( get_the_ID(), 'wpsb_meta_box_check', true );
if( $key == 'on' ) {
    get_template_part('templates/content', 'single-full');
} else {
    get_template_part('templates/content', 'single');
}
get_template_part('templates/footer');
?>