Небольшой простой пример:
<Grid HorizontalAlignment="Left" VerticalAlignment="Top">
<Grid.RowDefinitions>
<RowDefinition Height="1*"/>
<RowDefinition Height="1*"/>
</Grid.RowDefinitions>
<TextBlock HorizontalAlignment="Left" TextWrapping="Wrap" Text="Some text" VerticalAlignment="Top" Grid.RowSpan="2"/>
<Border BorderThickness="0,0,0,1" BorderBrush="#FF949494" >
</Border>
</Grid>