In my opinion, if you just started with Qt, it could be a good thing if you have the time to make a simple UI/Program that you all write manually, not using Qt Creator a single bit. I completely agree that Qt Creator is faster to build your UI, but you can learn more about the mechanics of the QWidget, QMainWindow, QLayout, etc. classes by doing it manually at least once. It could really help you if you get a problem to know a bit more details than to drag-and-drop widgets one on the other.
Of course, if you don't have any ideas on how to write a UI in Qt, you could create a simple UI in Qt Creator and look at how it is coded and try to reproduce something similar on your own.
Hope this helps.