Is there any good (and simple) document which explain step by step how to customize the Ribbon interface (Adding/Modifying) panels etc.?
The Revit Interface is pretty locked down. As far as I know, you can only add tools to the Add-In tab. That's done by installing into the REVIT.INI file in the program directory.
You can do some basic modification such as tearing panels off and moving them to a second screen etc. But that's about it. To play devils advocate for a second, some BIM managers that I know actually like this standardise interface as it means the same tools are available in the same place to everybody which makes for more consistant learning and helps in documentation.
Access a broad range of knowledge to help get the most out of your products and services.
Start with some of our most frequented solutions or visit the Installation and Licensing Forum to get help installing your software.
Upgrading to a 2015 product? Make sure to check these out 1st!