grid.cs

/* App.ScreenSize is obtained from the platform by DI */
// this code is completely untested!

public class MyGrid : ContentPage
{
    public class MyGrid()
    {
        var grid = new Grid
        {
            WidthRequest = App.ScreenSize.Width
        };
        
        grid.RowDefinitions = new RowDefinitionCollection
        {
            new RowDefinition {Height = 48},
            new RowDefinition {Height = GridLength.Star},
            new RowDefinition {Height = 48}
        };
        
        grid.ColumnDefinitions = ColumnDefinitionCollection
        {
            new ColumnDefinition {Width = App.ScreenSize.Width}
        };
        
        // create the 1/3 button
        var btnOneThirdWidth = new Button
        {
            HeightRequest = 44,
            WidthRequest = App.ScreenSize.Width / 3,
            Text = "1/3"
        };
        
        // create the 1/4 button
        var btnOneQuarterWidth = new Button
        {
            HeightRequest = 44,
            WidthRequest = App.ScreenSize.Width / 4,
            Text = "1/4"
        };
        
        // create the stacklayouts
        var stackThreeButton = new StackLayout
        {
            Orientation = StackOrientation.Horizontal
            BackgroundColor = Color.Wheat,
            Children = { btnOneThirdWidth, btnOneThirdWidth, btnOneThirdWidth}
        };
        
        var quarterStack = new StackLayout
        {
            WidthRequest = App.ScreenSize.Width / 4,
            Children = {btnOneQuarterWidth}
        };
        var stackFourButton = new StackLayout
        {
            Orientation = StackOrientation.Horizontal,
            BackgroundColor = Color.Yellow,
            Children = {quarterStack, quarterStack, quarterStack, quarterStack}
        };
        
        grid.Children.Add(stackThreeButton, 0, 0);
        grid.Children.Add(stackFourButton, 0, 2);
        
        Content = grid;
    }
}