Wow; I've never seen these before!

They look really nice, could work in quite a variety of settings, and your subdued paintjob certainly helps with that versatility.
Very nice project overall!
A shame GW did not pursue this avenue a bit more though; they are very useful pieces.
As an aside; did that range perhaps also include a fortress like structure with a small tower and a ramp in the 'back'? Because back in the day, my gaming club used to have exactly such a fortress, which I always loved. And a couple of years ago, I managed to buy one for myself. It's also made from hard foam, with a dark grey texture paint on top and some green flocking on the base of the walls (although the paint and flock could have been applied by the previous owner of course, but then again; the one in my gaming club looked exactly like it).
It has a very similar aesthetic to your buildings, and its material is also the same...