I'm posting these building templates as PDF files as I think they be more accessible than the JPG files. There is an album of the finished product so you can see what they could look like. I've copied the originals and used them to make a number of variations over the years.
As far as I know, the British company that published them is out of business and over the last 15 years, I've never been able to find them available commercially. If some one knows more than I do, please alert me and I'd be happy to send everyone to that location.
I print a color copy and use a glue stick to attach that to cardstock. Use a sharp Exacto knife. A dull one doesn't leave as crisp an edge. Cut the outside edge, making sure not to tear any corners. Lightly score the interior edges. The original templates have small triangular arrows indicating where to score the corners.
While some of the originals have tabs to turn underneath to secure the loose corners, I've found that they aren't really necessary. I simply hold the edges together while the glue dries. I use Krazy Glue, the Skin Guard version. It's more forgiving on the fingertips. I hold it with tweezers while I wait for it to bond, usually less then a minute.
Dealing with the seam can be a problem. What I've found is that once I get the best symmetrical rectangle/square on the shape of the walls, I sometimes have one side slightly longer than the another. I butt end and glue the shorter side into the longer. After it dries, I may need to slice off a fraction of the protruding edge. I have this happen more often with the chimneys than with the building walls. I've provided a variety of roofing material that I've collected from various websites over the years. Leave a slight overhang on all sides when measuring the size of the roof.
Before I attach chimneys, sheds or other additions, I use a extra fine point black Pilot pen to line the edges. When the building is bent to form the corners, the white of the cardstock underneath will show through. I like the definition the the black line provides. Looking down at a 6mm building, I think a sharp edge makes determining the line of sight easier during play. I know of another gamer who has dozens of colored markers to cover the white edges, so I think it's a matter of personal preference.
Not all of the chimneys will line up straight with all the models. After I bond the chimney, I test the angle of the pitch on the roof to determine if I need to slice a fraction off either the short or long end of the chimney base. Trial and error is the method I use. I've gotten better over the years.
The ruined inner shell is available on the original sheets. For the adaptations, I copy the flat color version onto black and white cardstock, making certain to keep it pale and at 90% of the original. I copy at 90% so the the outer shell will fit over the ruin. I keep the black and white pale so I can use colored pencils to shade some of the original color into the ruined version, and I do that after I cut the jagged edges but before I glue the walls.
Double strength cardstock works best for the base. Tracing around the base of the intact color version, I leave about 1/8" edge around the base. Again using the black pen, I sketch a rectangle or a square for the ruined floor, cross-hatching to give it depth. Then I glue the ruined walls to the base, sometimes leaving corners completely destroyed. Once it dries, I give the interior walls of the ruin a gray-brown wash for texture and use the black pen to shade smoke damage above and below windows and doors. I'll also add shell holes, bullet holes and other exterior damage.
I leave most of my buildings free standing, but they can be combined into streets or rectangular built up areas. The last step is to paint the outside of the base an appropriate latex brown, then shake some ground cover onto it while it's still set. Then I lightly spray a matte finish over both the ruin and the building.
Since some of the original buldings can be quite a challenge, I'd suggest starting with the sheds and cabins.