
Based on another I saw, our whelping box consisted of two sections, both 4 X 4 in size with a base and 3 ft sides. The first section we used until the puppies were up and moving around, and it was in a room where it was possible to fit a cot for one of us to sleep on at night. The initial section had pig rails and the front was a low piece, so mum could get out, but not the puppies (bearing in mind mine was a low to ground breed).
Once the pups were mobile, the original section was moved into the kitchen and the second section added, the low piece removed. The second section had a hinged door for access (mum). We always used a heat lamp as it kept the first section warm AND DRY. If mum was too hot, we'd drape a sheet across the back for her to get under.
The pups would naturally move from the initial section, which was covered with vet-bed and where they slept, to the new section which was covered with thick newspaper (collected locally from wherever I could find it!!) to toilet.