FUPanel.cs

using System;
using Windows.Foundation;
using Windows.UI.Xaml.Controls;

namespace MeasureScrewsArrange
{
	public class FUPanel : Panel
	{
		public FUPanel ()
		{
			for (int i = 0; i < 10; i++) {
				Children.Add (new Button {Content = i.ToString ()});
			}

		}

		protected override Size ArrangeOverride (Size finalSize)
		{
			int x = 10;
			foreach (var child in Children) {
				child.Arrange (new Rect (x, 0, 100, 100));
				x += 110;
			}

			return base.ArrangeOverride (finalSize);
		}

		protected override Size MeasureOverride (Size availableSize)
		{
			return new Size (Children.Count*110 + 10, 100);
		}
	}
}