Terrain material, layer blend help?

Hi guys,
Im new to creating materials and stuff like that but I watched a tutorial on youtube on how to create a material which will paint a texture onto a terrain depending on the slope. (heres a link

I have the material working as shown in the video but with a few extra maps such as specular, roughness, normals…and so on but Im having a bit of trouble trying to set up blend layers so i can start painting in dirt and whatnot. Just wondering if someone could give me some advice on how to modify this material?

Thanks