There is no way to give an meaningful estimate, mother than to find out what the local average for price per square foot is for the work you want done---add on/remodel versus new construction. If there is no plumbing, the cost should be lower. But, costs/fees for surveying, soil compaction(for foundation) and permits/etc. have to be considered. Sounds as if the plan would increase the value of the house to some extent. My personal belief is if a person wishes to spend decades in a home, has the money to spend without putting their finances upside down, and simply wants the home to be theirs and comfortable, who cares about resale value

Personal opinion and nothing else: Typically I'd say "make the bedrooms smaller -- I don't spend much time in there anyway"; however, in either situation, you're talking about small bedrooms -- is the master one of these small bedrooms? My kids have 12x12 rooms, and over the years my girls've had 1 twin ... 2 twins ... and 1 double ... but never anything bigger, and you're talking about smaller rooms! Add-on question: What kind of closets do these bedrooms have? A bedroom with plenty of good storage can be smaller and still be comfortable, whereas if your closet is modest, you need space for larger dressers and other storage. Having said that, if you're a typical 4-person family, I don't really see the point in having more than two bathrooms. They're expensive, high-maintenance rooms -- I want enough bathrooms for comfort, but I don't care to over-bath myself; I just don't enjoy cleaning toilets that much. An outside-the-box thought: If you'd JUST build the third bathroom for resale, you might consider leaving that room "empty" /use it as storage ... and in the future you'd have the option of finishing it off yourself ... or it could be presented to future buyers as "a room that could be renovated into a bathroom". That would also allow the future buyers the option of using that small space as a pocket office, a craft room, or whatever ... if it suited their purposes better. In conclusion, I suspect the 4/3 layout would be better for you at resale time ... but you're talking about trying to guess the mind of some unknown person, which is impossible. Build the one that'll suit your family best now.

Yes Helen that is the goal I am going for just a separate comfy living space that I can relax in that isn’t always in the eye of people who walk into my house. On our first floor we do have a separate office space for my husband as he works from home every day but on the occasion I do work from home it would be nice to work somewhere that isn’t my kitchen island or my dining table but since I don’t do it often I don’t need a dedicated office of my own, just a small desk in this space would work fine. Our main floor has: Living Room/Dining Combo Kitchen Office Bathroom Guest room (the guest room has a pullout couch in it with a tv). We entertain a lot during the holidays so we didn’t want this to strictly be a guest room so we could use it for extra entertaining space. I also have young nieces and nephews so it doubles as a guest room when they sleep over We also have a basement that is half workroom/laundry and the other side is finished which I have yet to do anything with besides storage. I don’t really want this space to be another guest room - I like the separation when guests stay over since there is another bathroom on the first floor and I have a room dedicated for guests already. I do like your idea of a coffee maker/mini fridge. Perhaps I could add a small bistro table with two chairs...

You lost me so maybe post some floor plans to scale. As for which is a better selling point IMO a master bedroom without a master bathroom is just a bedroom so find out what sells in your area I guess as for keeping track of your kids you know they will all grow and not want you to keep ttrack of them all the timeanyway.