We need five things in order to build your cart.

 1: The widest part of your dog. This can be the Shoulders, Belly or the Butt.
 2: The length of your dog from the back of the front shoulder to the end of the butt.
 3: The distance from the pelvic floor (this is the part of the dog that would rest on a bicycle seat; if they could ride a bike) to the ground, while your dog is in a normal standing position.
 4: The weight of your dog.
5: Color Pink or Blue
It is always nice to have the following, but these are not necessary.
Name, age, disability, Breed, Sex, Photograph of your dog.