How to create customer custom attribute for radio buttons, checkbox in magento 2

Create Extension and your setup file below
here customer=>namespace & Attribute=>Extension name

namespace Customer\Attribute\Setup;

use Magento\Eav\Model\Config;
use Magento\Eav\Model\Entity\Setup\Context;
use Magento\Eav\Setup\EavSetup;
use Magento\Framework\App\CacheInterface;
use Magento\Framework\Setup\ModuleDataSetupInterface;
use Magento\Eav\Model\ResourceModel\Entity\Attribute\Group\CollectionFactory;

class CustomerSetup extends EavSetup {

    protected $eavConfig;

    public function __construct(
        ModuleDataSetupInterface $setup,
        Context $context,
        CacheInterface $cache,
        CollectionFactory $attrGroupCollectionFactory,
        Config $eavConfig
        ) {
        $this -> eavConfig = $eavConfig;
        parent :: __construct($setup, $context, $cache, $attrGroupCollectionFactory);
    } 

    public function installAttributes($customerSetup) {
        $this -> installCustomerAttributes($customerSetup);
        $this -> installCustomerAddressAttributes($customerSetup);
    } 

    public function installCustomerAttributes($customerSetup) {


        $customerSetup -> addAttribute(\Magento\Customer\Model\Customer::ENTITY,
            'dropdown',
            [
            'label' => 'Radio Button',
            'system' => 0,
            'position' => 100,
            'sort_order' =>100,
            'visible' =>  true,
            'note' => '',


                        'type' => 'int',
                        'input' => 'select',
                        'source' => 'Magento\Eav\Model\Entity\Attribute\Source\Boolean',

            ]
            );

        $customerSetup -> getEavConfig() -> getAttribute('customer', 'dropdown')->setData('is_user_defined',1)->setData('is_required',0)->setData('default_value','')->setData('used_in_forms', ['adminhtml_customer', 'checkout_register', 'customer_account_create', 'customer_account_edit', 'adminhtml_checkout']) -> save();



        $customerSetup -> addAttribute(\Magento\Customer\Model\Customer::ENTITY,
            'multiple',
            [
            'label' => 'Multiple',
            'system' => 0,
            'position' => 100,
            'sort_order' =>100,
            'visible' =>  true,
            'note' => '',


                        'type' => 'varchar',
                        'input' => 'multiselect',
                        'source' => 'Magento\Eav\Model\Entity\Attribute\Source\Boolean',
                        'backend' => 'Magento\Eav\Model\Entity\Attribute\Backend\ArrayBackend',

            ]
            );

        $customerSetup -> getEavConfig() -> getAttribute('customer', 'multiple')->setData('is_user_defined',1)->setData('is_required',0)->setData('default_value','')->setData('used_in_forms', ['adminhtml_customer', 'checkout_register', 'customer_account_create', 'customer_account_edit', 'adminhtml_checkout']) -> save();


    } 

    public function installCustomerAddressAttributes($customerSetup) {

    } 

    public function getEavConfig() {
        return $this -> eavConfig;
    } 
} 

For Checkbox:

"type"     => "int",
"backend"  => "",
"label"    => "Test",
"input"    => "boolean",
"source"   => 'Magento\Eav\Model\Entity\Attribute\Source\Boolean',
"visible"  => true,
"required" => true,
"default" => "",
"frontend" => "",
"unique"     => false,
"note"       => ""