Sims 4 Build/Buy Tutorials

I'm a little confused by your request. Are you wanting to recolor an existing object, or do you want to make a new functional object? Or are you trying to make an EA related item (like a stove) and make it functional like all other stoves?

And do you mean recolor, or create a new texture for a new object? If you meant create a new texture, if you lookup Blender/mesh texture tutorials you can learn how to create the base texture in Blender, and other meshing programs, export the finished texture, finish details in Photoshop, and then import into S4S. To give it depth, texture, etc. you have to treat it like you're actually painting/drawing on the object (or find a texture on Google). And you can find object tutorials on Youtube, tumblr, etc., like this one or this one on S4S that goes over meshing, texturing, and importing, etc. into S4S.

If you want to make a functional CC object, like a stove, couch, etc., that already exists in EA's system that's fairly easy to do. You start the process like any other CC project, by finding an object close to what you want in S4S using the 3D Mesh option. You create, or import your already existing, mesh (hopefully similar in width, etc.) in Blender, import back into S4S, do your regular details like textures, etc. and if your object isn't too different from the one you cloned, you're pretty much done. If it varies, like the burners are farther apart than the original mesh, then you'll need to move the slots around so your sim will cook properly, but that's why people stick with similar sized meshes, etc. so they don't have to do that stuff. There are these two tutorials: Youtube tutorial and a written one, that go over objects like a table and a bed, but like I said it's a very similar process as a picture, deco object, etc.

If you mean a completely new object that doesn't exist in Sims 4, like a roller coaster, surfing, etc. with completely new animations, tuning, etc. then you're walking into a mostly undocumented minefield. We have one tutorial that goes over animated objects. That's it, and it's not a detailed one, video cuts out halfway through it, etc. I can give some guidance and misc tutorials that should help, but that's all I can offer until I make my own tutorials on the subject, or one of the few other functional object creators out there do so.