Here's the kit I started with; a second-hand HO scale house, possibly made by Faller, picked up from eBay:
I didn't want some Stalingrad-style ruin, but something that looked like it had been shot up in a gun fight. So step one was to break a few windows:
My original intention was to prise off all the existing window panes and cut up some thin clear plastic from a blister-pack to replace them, but they were stuck down too well and only breaking off in bits. In the end I decided to turn a flaw into a feature. The thick plastic windows left behind on the kit were broken in a way that I thought looked quite realistic, and I liked the grimy look of them, so I decided to keep them and build a new set of interior walls over them.
I raised the floor using an offcut of 4mm MDF to make the house more suitable for 15mm wargaming, and added plasticard batons to the walls. The batons are the same thickness as the clear plastic windows.
Next, I cut various pieces of plasticard to size, and added window holes to match those in the exterior wall. I fashioned some window frames from Plastruct's 'L'shaped beams. The interior walls, when placed over the batons, hide the clear plastic window parts behind them. Here's one I made earlier:
At this point I should mention that all the interior walls pictured above were only dry-fitted. When dry-fitting, I discovered that it was important to paint around the window on the reverse of both the exterior and interior walls with a dark colour before gluing them together.
If I hadn't done this, the unpainted plastic on the reverse of the interior walls would have been visible through the windows from outside, and vice versa.
Now for the bit that Abwehrschlacht might find interesting. I cut out one the windows altogether because it made the building look too much like some kind of sixties holiday home (which is probably what it was meant to be!), along with a section of the wall above it. I filed down my cuts to soften and round them and cut a piece of Slator's brick-embossed plasticard to the approximate shape of the hole. The embossed card is half the thickness of the model kit's walls so, when lined up with the inside of the wall, then it looks like the brickwork has been exposed behind the plaster.
On the inside, I added a few scraps of plasticard to represent a broken down door and another new interior wall:
Back to the front; the two pieces of the old wall and the new embossed card section are all glued onto the interior wall behind them:
I cut the new pieces of card slightly taller than they needed to be, then filed everything down to the same height. Here's the same view again, this time with two Peter Pig US Marines. As you you see, the building scales well with 15mm minis.
The next step was to fill the gaps between the two pieces of card. I used Das putty because I think it smells of marzipan, which I like. I put some over the brickwork and jabbed a biro nib into it a few times to simulate bullet holes. I didn't take any pictures of this bit so I'm going to be a tease and skip ahead to a later part of the build. The photo shows how it all looks after I block in the colours:
Well, that's it for now. Work is rather hectic again so I'll have to leave this project hanging...