After framing it out (you want to make sure there are no sharp objects anywhere on the inside of the box), it's time to add some posts to all four corners as well as to frame out a door. Now, with the sides of the box being 12" high, I'm not afraid of the pups being able to get out of the box for quite some time. However, I plan on fencing this all in as once the weather gets better, I'll move the box and place it outside for the pups to spend some time outdoors. I'll also cover it at that time to keep a beating sun or any other weather off of the pups.
As I wanted to keep the cost down to a minimum, I decided to use pine shavings as the base to keep it warmer and soft for the pups. I contemplated cedar shavings as I felt that would help keep the odor down some but thought that pine would act better in absorbing puppy messes. I still may get a small bag of cedar to add to help with odors.