<Window x:Class="LogicDesigner.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Designer" Height="300" Width="300">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="28" />
            <RowDefinition Height="1*" />
        </Grid.RowDefinitions>
        <Border BorderBrush="Black" BorderThickness="2">
            <Button x:Name="bt_rectangl" Margin="2" HorizontalAlignment="Left" Click="bt_rectangl_Click">Rectangle</Button>
            </Border>
        <Border BorderThickness="2"  BorderBrush="Gray" Grid.Row="5">
        <InkCanvas x:Name="MainForm" Background="AliceBlue" ActiveEditingModeChanged="MainForm_ActiveEditingModeChanged" EditingMode="Select" ></InkCanvas>
            </Border>
    </Grid>
</Window>

 private void bt_rectangl_Click(object sender, RoutedEventArgs e)
        {
            RectangleControl rectangleControl = new RectangleControl();
            MainForm.Children.Add(rectangleControl);
        }

<UserControl x:Class="LogicDesigner.RectangleControl"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Height="100" Width="100">
    <Grid>
        <Border BorderBrush="Black" BorderThickness="2">
        <Rectangle x:Name="rectangle">
            <Rectangle.BitmapEffect>
                <DropShadowBitmapEffect />
            </Rectangle.BitmapEffect>
            <Rectangle.Fill>
                <LinearGradientBrush StartPoint="0,0" EndPoint="0,1">
                    <GradientStop Color="#11FFFFFF" Offset="0"></GradientStop>
                    <GradientStop Color="Gray" Offset="1"></GradientStop>
                </LinearGradientBrush>

            </Rectangle.Fill>
        </Rectangle>
            </Border>
    </Grid>
</UserControl>