添加项目文件。

Sai.Toolkit.Revit/Assist/LevelAssist.cs

@@ -0,0 +1,16 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+using Autodesk.Revit.DB;
+
+namespace Sai.Toolkit.Revit.Assist
+{
+    public static class LevelAssist
+    {
+        public static SketchPlane GetLevelSketch(this Level level)
+        {
+            return SketchPlane.Create(level.Document, level.GetPlaneReference());
+        }
+    }
+}