Rice did a really cool grad project you might wanna check out.

https://www.youtube.com/watch?v=04hWW4--m-w

I actually toured this place, and it was really good for what it was designed to do. Specifically, it was meant to be a transition from the street to stability. It was 360 sq feet, 2 beds, no tub, no laundry, minimal personal storage space. Absolutely no privacy, either. But a good first step up. Also alot of the material was donated, so even though it was brand new, some of the wood paneling was already warping.

Here is another idea out of Austin.

https://www.iconbuild.com/

I am also trying to develop a sintered version. Using something similar to this:

http://mx3d.com/projects/metal/

How do you want to 3D Print the homes? Will they have "full size" or rather "Trailer Size"?

I dig this concept - not sure if it is still being printed, but you might want to check out the Homeless Guy blog and The Street Sheet in San Francisco, they both cover some unique challenges of the homeless population being mainstreamed that might be helpful.  If you are open to it, check out my project and maybe we could work together http://hackaday.io/project/4703-local-food-malls-with-global-impact  I also dropped a note on this project http://hackaday.io/project/4683-solar-refuge-and-recharge