There are few truly unique ideas in this hobby and this most certainly is not one either. Some considerable time ago I found a web site that espoused the use of foam board to use as the structural core to build structures. I have found it to be a quick way to build things and chose to use the method for a project that I am working on.
I have a small town developing in one corner of my layout. I have in mind a main street running sort of parallel to my tracks with the backs of the buildings made to look like run down tenements backing onto the track.
Outlined in the Red (the black lines were from a previous layout idea) you can see that I have an odd shaped quadrilateral space to fill just above the tracks.
Using foam core board and scraps of siding and brick sheet left over from other projects and kits, I have laminated on the store fronts for the main street.
The foam board gives me a sold structural base to build a row of 4 store fronts using bits of balsa wood and spare windows etc.
One thing I like about the foam board is that I can hollow out sections behind the windows to allow offset of the store images to give the impression of depth.
In this particular case the stores will be hardly visible as they face away from the viewer and will really only be seen at an angle from one location in the layout room. This method of construction is inexpensive and yields reasonable results for the location.