Creating a custom template for APEX can be problematic when you are not a web designer or when you do not have a lot (or any) experience with HTML and CSS. There is a very easy way to design in a "What You See Is What You Get" (WYSIWYG) way by using Adobe Photo-shop. In short it is nothing more then making a picture of how you want your application to look and slice it up into parts.
Here is a You-tube video that explains how to do this: