I'm having trouble trying to design a Class D Amplifier. Does anyone have any tips on where I can start?
I would recommend to start with the following two tutorials.
The first tutorial is to understand the big picture, the classification of amplifiers.  The second tutorial is to understand the principles, components required, and how to build the real thing.
(1) Amplifier Classes - Electronics Tutorials
(2) How to Build a Class-D Power Amp - Cezar Chirila, All About Circuits, 2018apr29