Took me a long time to figure this out, but got the answer on Stack Overflow
“In Visual Studio, the workflow I use when I want to design a new window is to add a Qt GUI class with Project->Add Class…->Qt4 Classes->Qt4GuiClass.
Then, fill out the form as necessary and the VS add-in will add the appropriate ui and moc files. Double clicking on the ui file will bring up Qt Designer, which you can use to lay your window out.”