An alternative to working with constraints in code using a nice fluent style interface. A work in progress, but hopefully helps

ConstraintsHelper.cs

	// // Just an example of making a fluent style interface. It's a work in progress but I'd rather not use the NSLayoutContraint code
	// // As it seems like a poorly designed API. I've wrapped it with some fluent style access for common issues
	// 
	//	var mainButton = new UIButton ();
	//	mainButton.SetTitle ("Click me dude", UIControlState.Normal);
	//	mainButton.BackgroundColor = UIColor.Blue;
	//	Add (mainButton);
	//
	//	var secondButton = new UIButton ();
	//	secondButton.SetTitle ("The other one", UIControlState.Normal);
	//	secondButton.BackgroundColor = UIColor.Red;
	//	Add (secondButton);
	//
	//	mainButton
	//		.ConstrainCenterXToParent (-100)
	//		.ConstrainCenterYToParent (0)
	//		.ConstrainWidth (150);
	//
	//	secondButton
	//		.ConstrainHeight (80)
	//		.ConstrainLeftToView (mainButton, 20)
	//		.ConstrainRightToParent (-10)
	//		.ConstrainTopToView (mainButton, 10);
	public static class ConstraintsHelper
	{
		public static void EnsureCorrectMode(UIView view)
		{
			if (view.TranslatesAutoresizingMaskIntoConstraints)
				view.TranslatesAutoresizingMaskIntoConstraints = false;
		}

		static void AddConstraint(UIView view1, NSLayoutAttribute attribute1, NSLayoutRelation relation, 
			UIView view2, NSLayoutAttribute attribute2, nfloat multiplier, nfloat constant)
		{
			if (view1 != null) 
				EnsureCorrectMode (view1);
			if (view2 != null) 
				EnsureCorrectMode (view2);

			var constraint = NSLayoutConstraint.Create (view1, attribute1, relation,
				                 view2, attribute2, multiplier, constant);
			view1.Superview.AddConstraint (constraint);
		}

		public static UIView ConstrainLeftToParent(this UIView view, nfloat gap)
		{
			AddConstraint (view, 
				NSLayoutAttribute.Left, NSLayoutRelation.Equal, 
				view.Superview, NSLayoutAttribute.Left, 1, gap);

			return view;
		}

		public static UIView ConstrainRightToParent(this UIView view, nfloat gap)
		{
			AddConstraint (view, 
				NSLayoutAttribute.Right, NSLayoutRelation.Equal, 
				view.Superview, NSLayoutAttribute.Right, 1, gap);

			return view;
		}

		public static UIView ConstrainTopToParent(this UIView view, nfloat gap)
		{
			AddConstraint (view, 
				NSLayoutAttribute.Top, NSLayoutRelation.Equal, 
				view.Superview, NSLayoutAttribute.Top, 1, gap);

			return view;
		}

		public static UIView ConstrainBottomToParent(this UIView view, nfloat gap)
		{
			AddConstraint (view, 
				NSLayoutAttribute.Bottom, NSLayoutRelation.Equal, 
				view.Superview, NSLayoutAttribute.Bottom, 1, gap);

			return view;
		}

		public static UIView ConstrainLeftToView(this UIView view, UIView otherView, nfloat gap)
		{
			AddConstraint (view, 
				NSLayoutAttribute.Left, NSLayoutRelation.Equal, 
				otherView, NSLayoutAttribute.Right, 1, gap);

			return view;
		}

		public static UIView ConstrainRightToView(this UIView view, UIView otherView, nfloat gap)
		{
			AddConstraint (view, 
				NSLayoutAttribute.Right, NSLayoutRelation.Equal, 
				otherView, NSLayoutAttribute.Left, 1, gap);

			return view;
		}

		public static UIView ConstrainTopToView(this UIView view, UIView otherView, nfloat gap)
		{
			AddConstraint (view, 
				NSLayoutAttribute.Top, NSLayoutRelation.Equal, 
				otherView, NSLayoutAttribute.Bottom, 1, gap);

			return view;
		}

		public static UIView ConstrainBottomToView(this UIView view, UIView otherView, nfloat gap)
		{
			AddConstraint (view, 
				NSLayoutAttribute.Bottom, NSLayoutRelation.Equal, 
				otherView, NSLayoutAttribute.Top, 1, gap);

			return view;
		}

		public static UIView ConstrainHeight(this UIView view, nfloat height)
		{
			AddConstraint (view, 
				NSLayoutAttribute.Height, NSLayoutRelation.Equal, 
				view, NSLayoutAttribute.Height, 1f, height);

			return view;
		}

		public static UIView ConstrainWidth(this UIView view, nfloat width)
		{
			AddConstraint (view, 
				NSLayoutAttribute.Width, NSLayoutRelation.Equal, 
				view, NSLayoutAttribute.Width, 1f, width);

			return view;
		}

		public static UIView KeepWidth(this UIView view)
		{
			AddConstraint (view, 
				NSLayoutAttribute.Width, NSLayoutRelation.Equal, 
				view, NSLayoutAttribute.Width, 1f, view.Frame.Width);

			return view;
		}

		public static UIView KeepHeight(this UIView view)
		{
			AddConstraint (view, 
				NSLayoutAttribute.Height, NSLayoutRelation.Equal, 
				view, NSLayoutAttribute.Height, 1f, view.Frame.Height);

			return view;
		}

		public static UIView KeepWidthHeight(this UIView view)
		{
			AddConstraint (view, 
				NSLayoutAttribute.Width, NSLayoutRelation.Equal, 
				view, NSLayoutAttribute.Width, 1f, view.Frame.Width);
			
			AddConstraint (view, 
				NSLayoutAttribute.Height, NSLayoutRelation.Equal, 
				view, NSLayoutAttribute.Height, 1f, view.Frame.Height);

			return view;
		}

		public static UIView ConstrainCenterXToParent(this UIView view, nfloat distance)
		{
			AddConstraint (view, 
				NSLayoutAttribute.CenterX, NSLayoutRelation.Equal, 
				view.Superview, NSLayoutAttribute.CenterX, 1, distance);

			return view;
		}

		public static UIView ConstrainCenterYToParent(this UIView view, nfloat distance)
		{
			AddConstraint (view, 
				NSLayoutAttribute.CenterY, NSLayoutRelation.Equal, 
				view.Superview, NSLayoutAttribute.CenterY, 1, distance);

			return view;
		}
	}