So directly from their web page (in case you cannot find the magazine):
Meryl Levin, describes how she made a dollhouse for her niece out of foam core board. She put graphic wrapping paper on the walls, cut clocks and pictures of out of catalogs and "framed" them with Sharpie, and her niece filled the rooms with her own toys. Not only is it almost as fun to personalize as to play with, it also stores flat, and can even travel with her to Grandma's house! If you want to try this yourself, here's how Meryl did it (use the diagram below as a reference):
1. Start with a piece of 20"x30" foam core board (a standard size at art-supply stores), and using a box cutter and a T-square or yardstick, cut 10 inches off of the longer end to make a 20"x20" square.
2. Cut the board horizontally right across the middle to create two 10"x20" rectangles.
3. Measure 10 inches across the bottom of one rectangle, and cut a notch 1/4-inch wide and 2 inches tall. At the top of the second rectangle, make a notch the same size.
4. At the bottom of both rectangles, measure 4 1/2 inches from both ends, and cut doorways 2 inches wide and 5 inches tall.
5. Slide the notches into each other to form the x-shaped house.
Someone commented that the noces need to be 6 and 4 inches, not two, so think about this if you try and make it. Have fun!