We have built a designer for the iOS storyboard format which is fully integrated into Visual Studio for Mac. The iOS designer maintains full compatibility with the storyboard format, so that files can be edited in either Xcode or Visual Studio for Mac. Additionally, the editor supports advanced features, such as custom controls that render at design-time in the editor.
A Storyboard is a visual representation of the appearance and flow of your application. Xamarin has introduced a Designer to allow Xamarin.iOS applications to take advantage of storyboards, so you can design your application screen visually and access the views, controllers and segues with C# for more control. You can also refer to this guide for an explanation and walkthrough of the Xamarin Designer for iOS
Covers working with the iOS User Interface in a Xamarin.iOS app including: the Appearance API, Creating User Interface Objects, Layout Options, Providing Haptic Feedback and Working with the UI Thread.
Xamarin.iOS exposes all the native user interface objects provided by Apple. They are easily added to Xamarin.iOS applications using the iOS Designer, Xcode's Interface Builder or programmatically. Regardless of which method you choose, Xamarin.iOS exposes all the user interface object properties and methods in C#.