Steven Mouzon has a thin 79p book on Katrina cottages available at Amazon ($3.95) - that would be where I would start if you're looking to build your own from plans.
From the Katrina Cottages site and The Guild Foundation:
Katrina Cottages aren't just great ideas anymore; many of them also include working drawings from which you can build your very own Katrina Cottage. You can find many of the Katrina Cottage designs for which there are working drawing on this site, but Katrina Cottage Plan Portfolios are now beginning to be released that contain some designs not currently carried here. And their variety is growing all the time. Katrina Cottage Types keeps track of all the variations.
The USA WEEKEND Katrina Cottage is a 523-square-foot "Kernel Cottage" designed to grow to 1,303-square-feet with the addition of two wings. Designed by New Urban Guild founder Steve Mouzon, the cottage was produced in a South Louisiana factory by Housing International Inc. and trucked to Maryland for USA WEEKEND's celebration of Make a Difference Day.
There's more in the October/November issue of New Urban News:
“It is unprecedented, to my knowledge, that a building type would be conceived, designed, and executed in four out of five planned delivery methods by such a diverse group of designers, builders, and manufacturers in one year’s time,” Mouzon told members of the Gulf-Urb listserve.
More at DCist: Darling Affordable Housing in Silver Spring
For the next several weekends in Silver Spring, you can get a close-up look at a different solution to the affordable housing dilemma, one that’s received tons of press coverage in the Gulf Coast in the last year: the Katrina Cottage. Conceived in response to the poorly planned, terribly designed, and often permanent trailer encampments erected by FEMA, several versions of the Katrina Cottage have been designed by New Urbanist architects. All have the same goal: to provide decent, inexpensive, easily constructed housing that complements a community rather than blight it. Sponsored by USA Weekend magazine, and supported by many of their Make a Difference Day volunteers, Silver Spring’s cottage is being constructed in the parking lot of a community center to maximize exposure. Upon completion, it will be moved to a nearby neighborhood for a local family to move in.
Wet Bank Guide's article on Katrina Cottages has NOLA photos.