Here's a video of their recent "abbey" project. As you can see, all the visible surfaces are painted insulation Styrofoam.
The other interesting source was Chris Walas, who builds whimsical fantasy scenes for his backyard railway. These are mostly foam and latex paint.
Some of his designs are really wild, like this Lemurian temple scene.
Okay, insulation foam and latex paint it is! Now I can move on to what I want to build. The commission is for a small craft shop with the owner's name on sign. It didn't take me long to think of Fiddler's Green paper models. Their two specialities are: aircraft and quaint buildings. I think this flower shop fills the bill nicely: it has a window for displaying some tiny craft creations, and a pleasant whimsical appearance. In its papercraft form, it's quite cartoony, but I'm not aiming for high realism in this model.
As a pleasant bonus, I got three free models for signing up with Fiddler's Green, so this cost nothing. (I will be signing up for the Fiddler's Green "Magic Key" subscription soon, because it seems like a very good deal.)
I've reached the next step, which is turning the model into a template so I can scribe the lines onto the insulation.
This model is going to involve a lot of bevelling edges down to 45 degrees so everything will fit together neatly, but I'm up for a challenge.