: Open Visual Studio and start a new C# Class Library project. Add References : Browse to your Revit installation folder. Add RevitAPI.dll (database functions). Add RevitAPIUI.dll (interface functions). Set Copy Local to False for both.

: Use uiApp.ActiveUIDocument.Selection to interact with what the user clicks.

[Autodesk.Revit.Attributes.Transaction(Autodesk.Revit.Attributes.TransactionMode.Manual)] public class MyCommand : IExternalCommand { public Result Execute(ExternalCommandData commandData, ref string message, ElementSet elements) { // 1. Get the Document UIApplication uiApp = commandData.Application; Document doc = uiApp.ActiveUIDocument.Document; // 2. Start a Transaction using (Transaction trans = new Transaction(doc, "My Customization")) { trans.Start(); // Your logic goes here (e.g., changing a parameter) trans.Commit(); } return Result.Succeeded; } } Use code with caution. Copied to clipboard 📝 Manifest Files (.addin)

: The primary way to "find" things in your model (like all Walls or Doors).

To help you move faster, would you like a code snippet for a (like auto-renaming levels) or a guide on debugging your code?