Let's back this up a bit...
I can tell that you need to know how to make a custom door. Are you talking about a parametric door that can have different modeled options and settings? If so, you will need to learn GDL scripting.
If not, and you only need to add parameters for the door's schedule data, I recommend the "Object Making with Archicad" PDF that is in your Help Menu. It has a pretty detailed explanation of making custom objects of different types.
You also asked about "linking the door into a schedule". Do you know how to make/use Archicad schedules? I ask because your phrasing really does not apply to Archicad. A schedule is a report of elements placed in your project based on criteria you set in the schedule. Any door that meets the criteria will be listed in the schedule.
Tom Waltz