Create a new module using silk software and check need Installing sql or php code and download the zip. After download open the sql file and paste the below code according with your modifications
<?php
/** @var Mage_Eav_Model_Entity_Setup $installer */
$installer = $this;
$installer->startSetup();
$this->addAttribute(
'catalog_category',
'my_custom_attribute',
array(
'group' => 'General Information',
'input' => 'select',
'type' => 'int',
'source' => 'eav/entity_attribute_source_boolean',
'label' => 'My Custom Attribute',
'required' => 0,
'unique' => 0,
'sort_order' => 3,
'user_defined' => 1,
'global' => Mage_Catalog_Model_Resource_Eav_Attribute::SCOPE_GLOBAL,
));
$installer->endSetup();