Starting with 3ds Max 2017, you can use the popular cross-platform development package Qt to create the user interface for your 3ds Max plug-in. See the maxsdk\include\Qt directory for headers exposing utilities for integrating Qt, as well as some customized Qt widgets used in the 3ds Max UI. Some of the standard plug-ins shipped with 3ds Max use Qt for their UI, and you can look at these in the SDK samples collection. Look at the maxsdk/samples/systems/sunlight project for an example of a plug-in that uses Qt for its UI. There is also a very simple sample located in maxsdk/howto/ui/qtObjectDemo.
The version of Qt required depends on the version of 3ds Max you are targeting. See the SDK Requirements topic for specific version information. Before you can create new plug-ins or build existing ones that require Qt, you need to download Qt, and install the Visual Studio 2017 Qt VS Tools add-on.
In Visual Studio, go to Tools > Extension and Updates ... > Online and search for Qt. Install the Qt Visual Studio Tools (2017) add-on. You will need to re-start Visual Studio.
The Qt Visual Studio Tools add-on determines the version and location of Qt for a project. Set this under Extensions > Qt VS Tools > Qt Options.