Some appraisers view closets, stairways, storage areas, enclosed patios, and other spaces differently, which can make a big difference in a large house. 

Without seeing how the door stairway is it is hard to cost estimate.

Animals should be in a carrier, or held by the handler in confined spaces such as elevators and stairways.

Walls, stairways, parking, etc.7. 

Hallways and stairways waste space so really try to minimize them. 

Taking this to the max would involve no stairways (because they waste space) and every room having a private entrance on each level with one kitchen and bathroom per level.

One looks like it has a stairway in it.

With that being said IF there was a fire in the kitchen and your tenant/roommate in that basement bedroom could not get out the stairway because of the fire and they die in your house, in your basement in what you knew to be an unsafe situation - how would you feel for the rest of your life about that?

I was able to turn that into a studio by enclosing the stairway from the main house and building an exterior stairway and deck. 

You can place "reasonable" restrictions on them, such as requiring a Veterinarian's health report; requiring spay/neuter to prevent aggressive behavior or commercial use; animal must be in a carrier or held when in confined spaces such as elevators and stairways, and leashed in common areas (unless this interferes with the task the animal performs, such as a seeing eye dog); handler must clean up after the animal in all common areas; handler must maintain sanitary conditions for the animal including no offensive odors emanating from the residence; animal must not disturb neighbors with nuisance barking or aggressive behavior; and you can require annual updates of both the "request for accommodation" letter and the Vet report.