Make custom block in custom module

custom.module

/**
 * Implementation of hook_block_info().
 */
function custom_block_info() {
  $blocks = array();
  
  	// Products overview
  	$blocks['product-overview'] = array(
    	'info' => t('Product overview'),
  	);
  return $blocks;
}

/**
 * Implementation of hook_block_view().
 */
function custom_block_view($delta='') {
  $block = array();
	global $language;
  	switch ($delta) {
    
    case 'product-overview':
  			$block['subject'] = t('Product overview');
	      $block['content'] = _product_overview();
		break;
  }

  return $block;
}

/* Product overview */
function _product_overview() {
  global $language;

  $query = db_select('node', 'n');
  $node_results = $query->condition('language', $language->language, '=')
          ->condition('type', 'product', '=')
          ->fields('n', array('nid'))
          ->execute();

  if ($node_results) {
    $nids = array();

    foreach ($node_results as $node_result) {
      $nids[] = $node_result->nid;
    }

    if (!empty($nids)) {
      $nodes = node_load_multiple($nids);

      $node_view = node_view_multiple($nodes, 'teaser');

      return array(
          array(
              '#theme' => 'overview_product',
              '#nodes' => $node_view['nodes'],
          ),
      );
      ;
    }
  }

  return NULL;
}

function custom_theme() {
  return array(
    'overview_product' => array(
      'variables' => array(
          'nodes' => NULL
      ),
      'template' => 'overview-product'
    ),
    
  );
}

overview-product.tpl.php

<?php
$max = count(element_children($nodes));
// Set up striping values.
$count = 0;
?>
<ul>
  <?php foreach (element_children($nodes) as $node) {
    	$count++;
  	  	$attributes = array();

  	  	$attributes['class'][] = '' . ($count % 2 ? 'odd' : 'even');

  	  	if ($count % 3 == 0) {
  	      $attributes['class'][] = 'third';
  	    }

        if ($count % 4 == 0) {
          $attributes['class'][] = 'fourth';
        }
  	?>
    <li <?php print drupal_attributes($attributes); ?>><?php print render($nodes[$node]); ?></li>
  <?php } ?>
</ul>