I think this is a Apache/Nginx problem here. You should not see /roadiz/web in your URL as the web root is meant to be web/ folder.
Then if you have a 404 error, that’s because you may have not setup your Apache/Nginx correctly to pass all requests to install.php controller. Check samples/ folder.
If you want to give a try, I suggest to use PHP internal server, it will be easier to launch it from scratch : https://docs.roadiz.io/en/latest/developer/first-steps/php_server.html