I cant help with the tutorial but I will elaborate a bit:D.
first here is a basic reference image (ignore how bad it is:p, its from an old test project).
as you can see the silver in the middle looks like metal but the blue paint/tyre tread doesn’t, basically anything you want to look metal is white or very light grey for dull/dirty metals and anything you want to be non-metal is black or in my case very dark grey because i wanted a little hint of metallic in the paint. you can also use low res textures for the metallic map as well instead of a full res version like I did in that pic.
hope that helps:)