We had to change the design of our large houses because UPS keeps lowering the maximum size that can be shipped ground. By making it with a flat top we were able to make the house smaller without taking away interior space from the cat. Add this option to a house and the outside dimensions will increase to 21"x21"x23" on the inside dimensions increase to 16"x16"x14"h. BUT IT WILL HAVE A FLATOP RATHER THAN A PEAKED ROOF. THE LARGE HOUSE STILL HAS THE STANDARD 6" DOOR(WOOD FRAME & VINYL FLAP UNLESS YOU UPGRADE. THIS OPTION CAN BE APPLIED TO Basic, Deluxe, Heated, Cedar, and Ultimate houses but not Econo, Pods, Multi-level or Tree Stump houses. MAKE IT LARGE flatop$49.00 Please note that some of the houses pictured through out this sight have various upgrades and add-ons,most of the houses do not come with a window unless you add it and the standard door is made of wood with a vinyl flap.Unless stated otherwise in the description. PLEASE READ ALL INFO ON THE HOUSES THOROUGHLY BEFORE PLACING YOUR ORDER. MOST PROBLEMS ARE CAUSED FROM PEOPLE WHO HURRY THRU THE STORE AND THEN MAKE UNINFORMED ORDERS. AT THIS TIME, CUSTOM HOUSES ARE SHIPPING OUT WITHIN 10 BUSINESS DAYS. NEED IT QUICK? CHECK OUT OUR READY TO SHIP HOUSES.