Here is an amigurumi pattern of a West Highland White Terrier that I designed to be my own Westie, Barry.

While Westies are typically white, you could make this pattern in any colour to change the look of the dog.

Almost any type of white yarn will work. I use what I have on hand which tends to be Impeccable, Red Heart Soft or Vanna. I typically use a 3.5mm crochet hook for most of of my ami - you can use whatever size hook you are comfortable with.