It took me a while to find this so I’m posting it so I don’t forget. Before I got my MacBook I was using a Mac Pro workstation with XCode already installed. It had a control in the toolbar titled "Page" with three options: Project, Build, and Debug.
When I installed XCode on my MacBook I lost the ability to switch between layouts. One of the things I don’t like working with XCode is how so many windows end up being displayed and the difficulty in finding and switching between them. The problem is exacerbated by the fact the MIB Editor is a separate program which is not integrated with the XCode environment. It’s too bad this All-In-One layout isn’t used by default, I may not have had such a bad first impression of the XCode UI.
I finally found how to restore my preferred 3-layout mode. Simply select All-In-One Layout in the General tab of the XCode Preferences. BTW, I searched using Google for "Customizing page control in XCode" to find this Apple documentation. I had found in the View menu "Show Page Control" which gave me a clue but the default page control only gives you Project & Morph. I though it odd that a control that has it’s own menu item, and that can contain different items, couldn’t be customized on it’s own.