It's pretty easy to build a warm house for your friendly neighborhood
ferals by using a styrofoam cooler or fishbox.

http://www.flickr.com/photos/ucl/set...582947/detail/

The guy (Ashot) lives not too far from me so I was able to attend a
demo he did last Saturday, building one from a cooler as well as using
formboard insulation. I used his ideas and built one on Sunday which
is almost done. I just need to paint it. I'll put up some pictures as
soon as I can.