WP block wp-admin based in user role

block-admin.php

<?php
add_action( 'init', 'blockusers_init' );
function blockusers_init() {
	//check if user is administrator
    if (! current_user_can( 'administrator' ) ){
		//check if it's wp-admin and not ajax calls
		if ( is_admin() && ! ( defined( 'DOING_AJAX' ) && DOING_AJAX ) ) {
			//redirect to home
			wp_redirect( home_url() );
			//exit after redirect is required
			exit;
		}
	}
}