<DockPanel Width="300" Height="300">
<Rectangle Fill="Red" Height="100" DockPanel.Dock="Top"/>
<Rectangle Fill="Blue" Width="100" DockPanel.Dock="Left"/>
<Rectangle Fill="Green" Height="100" DockPanel.Dock="Bottom"/>
<Rectangle Fill="Orange" Width="100" DockPanel.Dock="Right"/>
<Rectangle Fill="Gray" />