public void GroupedOperations(Autodesk.Revit.DB.Document document)
{
   // All and any transaction group should be enclosed in a 'using' block or guarded within 
   // a try-catch-finally blocks to guarantee that the group does not out-live its scope.
   using (TransactionGroup transGroup = new TransactionGroup(document, "Level and Grid"))
   {
      if (transGroup.Start() == TransactionStatus.Started)
      {
         // We are going to call two methods, each having its own local transaction.
         // For our compound operation to be considered successful, both the individual
         // transactions must succeed. If either one fails, we will roll our group back,
         // regardless of what transactions might have already been committed.

         if (CreateLevel(document, 35.0) && CreateGrid(document, new XYZ(0, 0, 0), new XYZ(0, 10, 0)))
         {
            // The process of committing of a group does not do anything to the already committed
            // transactions. They will stay available on the undo menu and may still be undone
            // individually. If it is not desirable if one transaction from a multi-transaction
            // operation can be undone by th end user, then the transaction group must be
            // assimilated instead of committed. See TransactionGroup.Assimilate for details.
            transGroup.Commit();
         }
         else
         {
            // Since we could not successfully finish at least one of the individual
            // operation, we are going to roll the entire group back, which will
            // undo any transaction already committed while this group was open.
            transGroup.RollBack();
         }
      }
   }
}

Public Sub GroupedOperations(document As Autodesk.Revit.DB.Document)
    ' All and any transaction group should be enclosed in a 'using' block or guarded within 
    ' a try-catch-finally blocks to guarantee that the group does not out-live its scope.
    Using transGroup As New TransactionGroup(document, "Level and Grid")
        If transGroup.Start() = TransactionStatus.Started Then
            ' We are going to call two methods, each having its own local transaction.
            ' For our compound operation to be considered successful, both the individual
            ' transactions must succeed. If either one fails, we will roll our group back,
            ' regardless of what transactions might have already been committed.


            If CreateLevel(document, 35.0) AndAlso CreateGrid(document, New XYZ(0, 0, 0), New XYZ(0, 10, 0)) Then
                ' The process of committing of a group does not do anything to the already committed
                ' transactions. They will stay available on the undo menu and may still be undone
                ' individually. If it is not desirable if one transaction from a multi-transaction
                ' operation can be undone by th end user, then the transaction group must be
                ' assimilated instead of committed. See TransactionGroup.Assimilate for details.
                transGroup.Commit()
            Else
                ' Since we could not successfully finish at least one of the individual
                ' operation, we are going to roll the entire group back, which will
                ' undo any transaction already committed while this group was open.
                transGroup.RollBack()
            End If
        End If
    End Using
End Sub