public class Grid : Panel

<Grid Width="300" Height="200" Background="Blue" HorizontalAlignment="Left">
    <Grid.RowDefinitions>
        <RowDefinition Height="40" />
        <RowDefinition Height="*" />
    </Grid.RowDefinitions>
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="70" />
        <ColumnDefinition Width="*" />
    </Grid.ColumnDefinitions>
        <!--Children here.-->
    </Grid>

Grid myGrid = new Grid();
myGrid.Width = 300;
myGrid.Height = 200;
myGrid.Background = new SolidColorBrush(Windows.UI.Colors.Blue);
myGrid.HorizontalAlignment = HorizontalAlignment.Left;

//We create and add the rows and columns:
//First column:
ColumnDefinition columnDefinition = new ColumnDefinition();
columnDefinition.Width = new GridLength(70, GridUnitType.Pixel);
myGrid.ColumnDefinitions.Add(columnDefinition);
//Second column:
ColumnDefinition columnDefinition2 = new ColumnDefinition();
columnDefinition2.Width = new GridLength(1, GridUnitType.Star);
myGrid.ColumnDefinitions.Add(columnDefinition2);

//First row:
RowDefinition rowDefinition = new RowDefinition();
rowDefinition.Height = new GridLength(40, GridUnitType.Pixel);
myGrid.RowDefinitions.Add(rowDefinition);
//Second Row:
RowDefinition rowDefinition2 = new RowDefinition();
rowDefinition2.Height = new GridLength(1, GridUnitType.Star);
myGrid.RowDefinitions.Add(rowDefinition2);

//Do not forget to add the Grid to the visual tree.