Random Custom Post Type Example from WCPDX

tweets.php

<?php

add_action( 'init', 'tweets_init' );
function tweets_init() {
	register_post_type( 'tweets', array(
		'public' => true,
		'labels' => array(
			'name' => 'Tweets',
			'singular_name' => 'Tweet',
		),
		'show_ui' => true,
		'supports' => array( 'title', 'excerpt', 'editor', 'thumbnail' ),
		'rewrite' => true,
		'has_archive' => true,
	) );
}

add_action( 'add_meta_boxes_tweets', 'tweets_add_meta_boxes' );
function tweets_add_meta_boxes( $post ) {
	add_meta_box( 'tweets_meta_box', 'Shoe Size', 'tweets_meta_box', 'tweets', 'normal' );
}

function tweets_meta_box( $post ) {
	$value = get_post_meta( $post->ID, '_shoe_size', true );
	echo '<input type="text" name="tweets_shoe_size" value="' . esc_attr( $value ) . '" />';
}

add_action( 'save_post', 'tweets_save_post', 10, 2 );
function tweets_save_post( $post_id, $post ) {
	if ( 'tweets' != $post->post_type )
		return;

	if ( defined( 'DOING_AJAX' ) || defined( 'DOING_AUTOSAVE' ) )
		return;

	if ( ! current_user_can( 'edit_post', $post_id ) )
		return;

	if ( ! isset( $_POST['tweets_shoe_size'] ) )
		return;

	$value = floatval( $_POST['tweets_shoe_size'] );
	update_post_meta( $post_id, '_shoe_size', $value );
}

/*

$query = new WP_Query( array(
	'post_type' => 'tweets',
	'meta_query' => array( array(
		'key' => '_shoe_size',
		'value' => '5',
		'compare' => '>',
		'type' => 'NUMERIC',
	) ),
) );

var_dump( $query->posts );

*/