Dear Paul,
Cool that you worked with AutoLISP and ARX. So did I. Don't expect that to help you learn Revit programming, though.
The Revit API is very small and simple, with a twist.
The most important things to understand about of Revit programming are:
- You need to understand the product first, from an end user point of view, or the API will make no sense at all.
- Realise that the Revit API is entirely event driven. You can only use it in a valid Revit API context, and the valid context is only provided within the event handlers.
Here is everything you need to get started using the Revit API:
http://thebuildingcoder.typepad.com/blog/about-the-author.html#2
Here is everything you need to understand how to implement the external event:
http://thebuildingcoder.typepad.com/blog/about-the-author.html#5.28
I suggest you start from that end and get hold of some sample models to test in.
Implement a dummy window area percentage calculator for starters.
Once you have that in place, ask a new question here in the forum about implementing the window area percentage calculator for real.
Before doing that, discuss with some application engineers and product usage experts how that calculation should be approached manually.
That will help decide how to address it programmatically.
Good luck, and have fun!
Cheers,
Jeremy