You can search the links I gave for "Lodging." Yes, the answers are there.

""We just put $150K into renovating the carriage house, what can we deduct?""

You get to include this as Basis against the future sale. There is no Deduction for improving property.

"I am not sure if this is compensation or a fringe benefit"

Or Neither...

"and what taxes it may be subjected to."

Or None.

"It is a separate structure so it is not renting a room"

Renting a Room isn't the same as calling this Rent, or for the convenience of the employer as part of the job. You seem focused on the property, not the relationship.