Very big door check your existing door or wall to see if there is space the internal flap needs to slide in from above.

New Staywell PetSafe 660 Extra Large Aluminium Big Flap Dog Door

Description
Aluminium Extra Large Pet Door - White
White finished heavy duty Aluminium with flexible flap.
Suitable for dogs up to 45kg
Heavy Duty Aluminium Frames
Plastic Locking Security Barrier

 

Dimensions
Suitable for all doors up to max 2" (50mm)
Overall size : 692.6mm x 417.1mm, (27 1/4" X 16 7/16")
Cutout Size : 642mm x 366mm, (25 1/4" X 14 3/8")
Pet Max shoulder width : 352mm, (13 13/16")