To build a basic DIY whelping box, you will need either a kiddie pool, cardboard box, or a storage bin. You should also stock up on bedding material like blankets, towels, or crate pads. Start by measuring the mama and opt for a box or pool that's comfortable for the mama to relax with the pups. Next, line the bottom of the box with your chosen bedding material. This will help to keep the puppies warm and dry. Finally, place the box in a quiet, private area where your dog can feel safe and secure. By following these simple steps, you can easily create a cozy space for your dog to welcome her new puppies into the world.