GUI Design in Slicer 5.x

Despite not being very familiar to Slicer I am given the task of designing a custom GUI to ease the use of Slicer by physicians. I want this GUI to be run in Slicer 5.x. I read about Slicelets and my task is the exact definition of them. However, I am having trouble understanding the simple example provided by following link:

Furthermore, I am not sure if it will work on Slicer 5.x. I am searching the new documentation however there is not an up-to-date page describing GUI design. I humbly ask for a guide that you think might be helpful for my relatively simple task.
Thanks a lot in advance.

This is an important topic.

You can enable “Developer mode” in Slicer Settings:


then use the QT designer to make a prototype of a GUI.

You may also want to check out this interesting thread dealing with Slicer QR.