Are you thinking Susan Susanka? (I think that's how you spell it). The Not so Big House Book.

There's a website, too:

http://www.notsobighouse.com/

Sarah Susanka. Ichabod I kept calling her Susan when I first read the book.

I haven't looked at Susanka's books for a long time, but I did reference them when I got started with our 1200 square foot house. I didn't find her books that helpful for our project. I might not be remembering it correctly, but it seems like her homes were in the 2000-2500 square foot range which is the size house we downsized from.

My best resources were blogs (particularly the architect couple's 860 square foot house at Chezerbey.com) and the NKBA accessible guide for kitchen and bathroom minimums, recommendations and ADA dimensions.

I think he'd get some great ideas looking at the "Small Cool Contest" submissions at Apartment Therapy. Here's a link to 2015's Small Cool Contest Winners. Entries include floor plans and there are tons of submissions and probably six years worth of them

Rachel, I thought of two more small homes:

Assortment Blog 665 square feet

Jessica Helgerson's Sauvie Island 540 sq ft home

Not a book, but a website. Incredible small homes are being built in Vancouver. Smallworks He'll find lots of inspiration there. Of course there are all the Tiny house builders as well. Although they are smaller, there are ideas that could translate into a slightly larger space. check out Tumbleweed, Brevard Tiny House, Wishbone.

And Ross Chapin has a few under 500

http://rosschapin.com/plans/cottages/

I am not a fan of Suskana's books. Just not.

Here is a great sit http://www.solardecathlon.gov. These are houses college students have designed and built for a contest put on by the Dept of Energy. There are lots of pictures, layouts, and good info about energy efficiency.

There are lots of good tiny house blogs. Even though tiny is smaller than what he is looking at there is still lots of good info there. Tinyhousetalk.com and smallhouseswoon.com are two of my favorites.

Also I love the ADU houses in the NW. There are lots if builders and architects in Seattle and Vancouver especially with beautiful ideas.

Christopher Lowell has some creative ideas on designing and making small spaces work.

Small Spaces