Objective-C class for placing UI elements based on screen size
Some thoughts on it:


Code: I'd suggest to create a Category on UIScreen. This is even more elegant than creating a separate class.
Naming: In Objective-C getter usually do not have the prefix "get".
General approach: Without knowing the background of your app and any detailed implementation, it's not common to layout UIViews relatively to the screen. As you're using UIViewControllers, any additional view should be added as a subview to the UIViewController's view. This ensures that layout and orientation changes are handled for you and are automatically being applied to all subviews by the UIViewController.