how to generate custom procedural terrain ?

hey guys so I'm making an endless low poly runner so I want to use a noise map that will keep changing and generate low poly terrain each time that the start of it could fit the end of the old one and I want to modify the noise map so that it gives me every time a flat small piece of terrain in the middle so that I can keep spawning road on it I'm completely clewless on how to do that thank you so much