You can customize a lot of the templates yourself by editing the .css rules and replacing images. But if you want a completely custom design, then you will need to be really experienced and know a lot of web design. You would probably have to study a book on web design and php.
You want to create or you want to use? Big difference. If you want to use and don't mind spending a few dollars get Thesis and learn how the "hooks" work... it's is extremely customizable. If you want to create templates from scratch there are some very good tutorials on line which you can find by searching for them. The best place to start is at the WordPress site... read all the Docs http://codex.wordpress.org/Using_Themes