When my Norfolk Terrier was pregnant I browsed the web to see how to build a whelping box. A whelping box gives the dam an opportunity to have some peace and quiet when she gives birth to her puppies (known as whelping). Most of the information I found was how to build a wooden whelping box for a much larger dog or cardboard whelping boxes that you could buy over the net. However none of these met my requirements.
I had read several books from experienced breeders which stated that if you had two sections to the whelping box it allowed the puppies, as they got older, to form good habits in relation to being house trained. In essence the design of the box would be a pre-school to crate training.