Mother-in-law suite vs bedroom, bath, laundry

[Glenda Powers]

I'm building out my basement to include a rental space.  Due to zoning, I could not have a full kitchen without going duplex and that added too much expense to the build.  

I'm adding 750 square feet with the basement build, with 280 of that going to the what I term a MIL suite.  It will have a bar kitchen, with laundry, and full bath and bedroom.  The square footage of the suite is 280.  My numbers are not jiving because I think the 750 is outside building measurements and doesn't include the room used up by stairs and walls.  When I do the square footage wall to wall, using the designer drawing measurements, I come up with 574 total.

I'm trying to determine if my feelings are correct that this space is worth more as as self-contained rentable space that could either be used as a MIL suite, or man cave compared to simple square footage with all the components.

Of course, the added bedroom, bathroom and laundry are key components...but I'm not so sure about the sink, fridge, and convection oven adding that much to it.

Is there a known formula that I can apply to this scenario?  I'm certain the region is good for renting the space as well (close to colleges, and hospitals, and in particular geriatric facilities) but I think perhaps the MIL is probably not a good one as the driveway is uneven and probably more prone to falling for the elderly.

My goal for this analysis is to determine how much increased value to add for a sale of the house.  I plan to hold and rent the basement in the short term, but thinking on selling.