I started out with the Midwest Crate (I524) 24"X18. It had a divider panel, so we scaled it down to fit our puppy. I kept looking at the Potty Training Puppy Apartment - but it seemed costly for it's purpose. I had to leave my baby for a weekend and I was nervous about "Daddy" waking up to take her out for her late night run - so I broke down and bought the apartment. Our baby girl LOVES her apartment - she just turned 5 months old and she tucks herself into bed at night. There's a little door in the apartment that leads to the "potty" and she figured it out on the first night. I'm a believer now! Potty Training Puppy Apartment is a great way to go. Check it out.
Modern Puppies - Potty Training a Puppy