Permit a new bedroom?

[Mary Spalding]

Hi All,
I have searched for an answer specifically to this question, so if my searching skills are poor, I do apologize.

On my latest SF home, it has an attic area over the porch that has a wonderful space that will be able to add a 15x20 bedroom w/ closet.
I have a great GC, but he has hinted at not getting it permitted. He said that inspectors can be a hassle, etc and will open a "can of worms" with other issues.

My husband and I do not agree. We are holding his home for a rental and think we should pull permits. Our local assessor views bedrooms as not adding value to the assessed price, only sq footage to a home or a bathroom and this space is already included in the current foot print.

But for resale value, if we ever sell it or for appraised and rentability value, we think we should permit it.

What are the pros and cons of it?

Any ideas would be appreciated.