Title sayy everything.
how do I create a noise texture for my material/landscape ?
I want to make my own, don’t want to import someone elses noise texture
Depends on what program you use and what type of noise you want. For example, if you want static looking noise in photoshop, in a new canvas in a power of 2 (1024x1024 / 2048x2048 etc) click on filter then noise. Adjust the size and the box for monochrome or colours.
UE4 also has noise nodes you can use in realtime (expensive) or use them to render to texture and save it for later use (cheap).
Here’s a UE4 blog post on basic usage Getting the Most Out of Noise in UE4 - Unreal Engine