I chose the largest 46" size for my 3 cats (room to accommodate a large litter box, dishes, and the 3 cats). It is fairly well constructed but the sides have a tendency to bow in after a short time. I love the zip-off top and convenient roll-up door but the bottom is NOT waterproof and does NOT zip off which makes cleaning rather difficult. I have also noticed the material seems to be wearing much more quickly than anticipated. If you have active pets this pen may not be the best option.