Dear Sylvain,
Are you aware of RevitLookup and the BipChecker?
if not, please check them out. They are described in many discussion threads here in the forum and also by The Building Coder.
In fact, installing and using RevitLookup is one of the very first things to do when getting started with the Revit API, and is covered by the getting started material and the DevTV and My First Revit Plugin tutorials:
http://thebuildingcoder.typepad.com/blog/about-the-author.html#2
RevitLookup enables you to interactively explore the values of the parameters attached to each Revit BIM element.
You can use that information to explore what data to access, where and how.
I hope this helps.
Best regards,
Jeremy