add your own choices using symfony choice type code example

Example 1: choice type symfony

use Symfony\Component\Form\Extension\Core\Type\ChoiceType;
// ...

$builder->add('isAttending', ChoiceType::class, [
    'choices'  => [
        'Maybe' => null,
        'Yes' => true,
        'No' => false,
    ],
]);

Example 2: creating your own symfony choice type

// src/Form/Type/PostalAddressType.php
namespace App\Form\Type;

use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\Extension\Core\Type\TextType;
use Symfony\Component\Form\FormBuilderInterface;

class PostalAddressType extends AbstractType
{
    // ...

    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add('addressLine1', TextType::class, [
                'help' => 'Street address, P.O. box, company name',
            ])
            ->add('addressLine2', TextType::class, [
                'help' => 'Apartment, suite, unit, building, floor',
            ])
            ->add('city', TextType::class)
            ->add('state', TextType::class, [
                'label' => 'State',
            ])
            ->add('zipCode', TextType::class, [
                'label' => 'ZIP Code',
            ])
        ;
    }
}