Custom Top Level Navigation

Hello experts,

I have specific UI Graphic Design for the Top Level Navigation of the portal, in funtionality it is like SAP EP standard, a 2 level navigation bar. Still it's quite different because of the look and feel. Currently I'm creating a theme, and customizing the top level navigation, meanwhile I'd like to have other otions in case this approach does't work to fulfill the requirement, I'd like feedback and documentation abount creating a new top level navigation from scratch, or to create a copy of the standard and extend it the way we need it. I hope you guys can help me out.

Thanx in advance.

JV