A simple, fairly un-opinionated starter abstract class and subclass example, for generating user meta in WordPress.

user-meta-starter.php

<?php
/**
 * Plugin Name: User meta starter class.
 * Plugin URI: https://dennys.com
 * Description: User meta
 * Author: ramiabraham
 * Version: 1.0
 * Text Domain: user-meta-starter
 * Domain Path: languages
 */

// Exit if accessed directly
if ( ! defined('ABSPATH') ) {
	exit;
}

/**
 * Copy or extend below
 */
abstract class User_Meta_Starter {

    public $fieldset_title;

    public $field_1_title;
    public $field_1_key;
    public $field_1_type;

    public $field_2_title;
    public $field_2_key;
    public $field_2_type;

    public $field_3_title;
    public $field_3_key;
    public $field_3_type;

    public function __construct() {
        $this->set_fields();
        $this->init();
    }

    abstract public function set_fields();

    public function init() {
        add_action( 'personal_options_update',  array( $this, 'save' ) );
        add_action( 'edit_user_profile_update', array( $this, 'save' ) );
        add_action( 'show_user_profile', array( $this, 'profile_fields' ) );
        add_action( 'edit_user_profile', array( $this, 'profile_fields' ) );
    }


    public function save( $user_id ) {
        update_user_meta( $user_id, $this->field_1_key, sanitize_text_field( $_POST[ $this->field_1_key ] ) );
        update_user_meta( $user_id, $this->field_2_key, sanitize_text_field( $_POST[ $this->field_2_key ] ) );
        update_user_meta( $user_id, $this->field_3_key, sanitize_text_field( $_POST[ $this->field_3_key ] ) );
    }


    public function profile_fields( $user ) {
        ?>
            <h3><?php echo sanitize_text_field( $this->fieldset_title ); ?></h3>

            <table class="form-table">
                <tr>
                    <th><label for="<?php echo $this->field_1_key; ?>"><?php echo sanitize_text_field( $this->field_1_title ); ?></label></th>
                    <td>
                        <?php if ( $this->field_1_type === 'text' )  { ?>
                            <input type="text" name="<?php echo $this->field_1_key; ?>" value="<?php echo esc_attr( get_the_author_meta( $this->field_1_key, $user->ID ) ); ?>" class="regular-text" />
                        <?php } else { ?>
                            <textarea rows="5" cols="30" name="<?php echo $this->field_1_key; ?>" value="<?php echo esc_attr( get_the_author_meta( $this->field_1_key, $user->ID ) ); ?>" class="paragraph-text" />
                                <?php echo esc_attr( get_the_author_meta( $this->field_1_key, $user->ID ) ); ?>
                            </textarea>
                        <?php } ?>
                    </td>
                </tr>

                <tr>
                    <th><label for="<?php echo $this->field_2_key; ?>"><?php echo sanitize_text_field( $this->field_2_title ); ?></label></th>
                    <td>
                        <?php if ( $this->field_2_type === 'text' )  { ?>
                            <input type="text" name="<?php echo $this->field_2_key; ?>" value="<?php echo esc_attr(get_the_author_meta( $this->field_2_key, $user->ID ) ); ?>" class="regular-text" />
                        <?php } else { ?>
                            <textarea rows="5" cols="30" name="<?php echo $this->field_2_key; ?>" value="<?php echo esc_attr( get_the_author_meta( $this->field_2_key, $user->ID ) ); ?>" class="paragraph-text" />
                                <?php echo esc_attr( get_the_author_meta( $this->field_2_key, $user->ID ) ); ?>
                            </textarea>
                        <?php } ?>
                    </td>
                </tr>

                <tr>
                    <th><label for="<?php echo $this->field_3_key; ?>"><?php echo sanitize_text_field( $this->field_3_title ); ?></label></th>
                    <td>
                        <?php if ( $this->field_3_type === 'text' )  { ?>
                            <input type="text" name="<?php echo $this->field_3_key; ?>" value="<?php echo esc_attr(get_the_author_meta( $this->field_3_key, $user->ID ) ); ?>" class="regular-text" />
                        <?php } else { ?>
                            <textarea rows="5" cols="30" name="<?php echo $this->field_3_key; ?>" value="<?php echo esc_attr( get_the_author_meta( $this->field_3_key, $user->ID ) ); ?>" class="paragraph-text" />
                                <?php echo esc_attr( get_the_author_meta( $this->field_3_key, $user->ID ) ); ?>
                            </textarea>
                        <?php } ?>
                        </td>
                </tr>
            </table>
        <?php
    }
}

/**
 * Customize
 */
class User_Meta_Custom extends User_Meta_Starter {

    public function set_fields() {

        $this->field_1_type = 'text';
        $this->field_2_type = 'text';
        $this->field_3_type = 'textarea';

        $this->fieldset_title = __( 'Here are some fields', 'user-meta-starter' );

        $this->field_1_title  = __( 'Here is field one.', 'user-meta-starter' );
        $this->field_1_key    = 'user_meta_starter_1';

        $this->field_2_title  = __( 'Here is field two.', 'user-meta-starter' );
        $this->field_2_key    = 'user_meta_starter_2';

        $this->field_3_title  = __( 'Here is field three.', 'user-meta-starter' );
        $this->field_3_key    = 'user_meta_starter_3';
    }
}
new User_Meta_Custom;