-About 40% of couples sleep in separate rooms. Play on that statistic. 

-Do you need two master suites? 

-This MBR has its own master bedroom!

-MBR with its own "snoring" room.

-Master suite with private office.

-Separate room for caretaker.

-Private media room close by.

"Flex space - can be used as an office, nursery, study, etc."

Call it the ultimate in flex space and describe its various potential uses.

It is a bonus to have two MBRs.

Master Bedroom Retreat.

Owners retreat

Sounds like a multi-level house. Separate room could be a retreat (we see that here) or simply a bonus room.  Office? Den?

Bonus room suitable for many uses. 

Owner suite sounds good.

However, the challenge is to define the space to prevent and interested buyer from confusing themselves with the question "What would I do with this space?"  When they ask themselves that question, the pass of the opportunity.

Make sure your staging exhibits the 'transformation in lifestyle' a move-up buyer is seeking.  That will be mostly dictated by lifestyle  of folks with the income level to live in that house.  For example, a private art gallery for a $70,000 annual income won't work.

An infant nursery, a Hemingway room, even en-suite could all suggest the transformation a buyer pursues. Please don't stick a bed in it and call it done.

  Separate MBR suite. 

   My question, was the addition permitted and in compliance with building codes?

Ante chamber or drawing room.  Toured a lot of castles last month and they had these "drawing rooms" so the ladies could withdrawl after dinner to talk about ladylike things while the men drank and smoked.  Ante chamber or waiting room could also work.  Hard to tell w/o a floorplan.

Love Nina Hollander answer

I'm not really wrapping my mind around your description. Is the additional level above the top level? You said it was detached from the rest of the house. Perhaps a master retreat or an executive master suite but I need to see.

Depends on how you  decorate it depends on what to call it.

Multi-level?  Because it is.

David Martin (703) 585-4687 - now when Margaret Rome, Baltimore Maryland says so... I can't add anything to that!

Master wing

Master Bedroon Suite looks good for me.

Modified or Customized Split Level.

Sounds nice,

What is your idea for that room? Maybe a bonus room?

I would call it flex space too.

Call it a master suite bonus with use left to the imagination!

In our MLS it would be just another living area.

if the additional level is on top of the split entry, it would then be called a colonial... it has two full levels of home.... two row of windows in front?????

a photo would have been easier ...

Downstairs Master Bedroom.

Doghouse, for when the wife is angry at the husband, again.

Owner selective living, sleeping programmable quarter.

Office; if there already is one - his and hers office, that became popular. For a young couple, a nursery might work too.

I would be nice to see a photo.  This could be in-law or out-law quarters, Bonus Master Suite with Office or meditation room.  You want to market the space for the many ways you feel it would be best used for in your market.  
 

Debe Maxwell, CRS nailed this one!

Two master br suites. 

I am seeing many splits and raised ranches here where they have added another level. Most though have been a madter suite, bath, walk in and another bedroom on the other half. Twin maseters, bonus, flex, the terms are many depending how it is decorated and used

The ultimate great room.

How about a bonus room?