Security is a huge concern when sharing space.

[Roger Simons]

Nobody seems to be addressing the elephant in the room.  If you want good revenue you must maximize the space you have.  Duh. 
The more people you can rent to the more money you pull in each month and the more your property is worth.  Duh.
Anyone with valuables isn't going to live with strangers with no security.  Lots of people don't need huge amounts of space but they don't want to worry that anyone can easily take what they have there.  
Another problem with people living closer together is noise disturbance. 

The solution to both is to devise some sort of pod structure that uses a loft bed where the bed is over the desk, perhaps on a pulley system to raise it to the ceiling during the day.  Even a single bed takes up quite a bit of space (about 40" x 78") so that means a large desk/storage area under that bed if the space is utilized well.  The desk doesn't have to take up the whole length obviously.  It could also be a wrap around design as most desks aren't 40" deep.  Height adjustable, slideout shelves could be used for storage.

You want natural light obviously. So the (double) walls would need to let light in from the window.  Light should come from above and inside the pod light colored finishes could be used to reflect/disperse the light well.  If the light comes from above
The pod would need to be ventilated (HEPA filtered for superb air quality) from that same window.  Realize that this means that person would sleep in dead silence meaning excellent sleep quality.  This is the biggest problem with sharing:  Sleep interruption because of noise.  Most people use alarm clocks to wake up!

The challenge is how to make it secure.  Glass can be easily smashed (plexiglass is strong but too expensive) but there could be a steel grid framework with glass panels.  If the grid is small enough (say 12" x 12"?) no one could get in, even if the glass was smashed.  Small valuables could be secured in a lock box.  As long as someone can't reach the lockbox by sticking their arm in through smashed glass, you're safe.  Plus realize that in a house like this someone is usually home.  It could be alarmed.  This makes it very secure.  Rigging up a steel and glass structure wouldn't be cheap but it sure would make a huge difference to the quality of tenant you get.  One plus would be the glass may be acquired as scrap as offcuts being we are using small panes!  The steel would have to be welded, no getting around that.  It would have to be able to be disassembled.  This would compromise security a little but it would take a while to dismantle after drilling out the bolts.  

One issue with basement dwellings is they often use a 7' ceiling.  This makes it a problem for taller people and a normal thickness of mattress and the structure supporting it.  For this it would absolutely need to be on pulleys but even this would challenging.  Thankfully there are lots of shorter people that need accommodation too!  

So if you have any ideas about a security pod, please respond.