Are you planning to place the pen inside or outside the house? This aspect matters since it will determine the type of materials you will need to focus on. If you put the pen indoors, you want to add a mat to it in case of accidents occur. Puppies are not great at holding it in, and they relieve themselves whenever they have the chance. Placing a mat and some training pads eliminates the issue of cleaning around the floor and the carpets. Food and water spills are also prevented. If the pet pen is outside, consider a covered model to protect the little one from the sun.