//declare variables
RowDefinition RowDef;
StackPanel StackP;
TextBlock TextB;

//Add 10 rows to Grid
for (int i = 0; i < 10; i++)
{
    //Define new Row to add
    RowDef = new RowDefinition();
    RowDef.Height = new GridLength(100);

    //Add row definition to Grid
    MyGrid.RowDefinitions.Add(RowDef);

    //Define the control that will be added to new row
    TextB = new TextBlock();
    TextB.Text = "Row: " + i.ToString();

    //create stackpanel and define which row to add the stackpanel to
    StackP = new StackPanel();
    StackP.SetValue(Grid.RowProperty, i);

    //add your control to the stackpanel
    StackP.Children.Add(TextB);

    //add the stackpanel to the grid
    MyGrid.Children.Add(StackP);
}