Windows lets you easily see how much space is used on your hard drives, but there's no convenient way to see what is taking up that space. While accounting for all those bytes remains an issue in Windows 8, you can at least see how space-hungry your Metro apps are.
As this article on LostInTechnology notes, getting a summary of installed Metro apps and their drive usage isn't difficult. Just hit Windows+C to bring up the Charm Settings bar and select "Change PC Settings". In the new window, choose "General" in the left-hand panel and then click "View app sizes" in the right panel.
You'll then see a list of installed apps in descending order of size, similar to the view in iOS' General settings.
Check How Much Space Each Modern UI App is Using in Windows 8 [LostInTechnology]