* Plasticard (I used 0.25, 0.5mm and 2mm thickness)
* Polystyrene cement
* Green Stuff
* Spare CDs or other things to use as bases
Grab yourself a bit of cardboard. A cereal box would be fine. Mark yourself a square with sides of 3" (75mm), and cut it out. Find the midpoint of each side, mark half an inch (12.5mm) either side of this, so that there is an inch (25mm) marked in the middle of each side. Trace lines between these so as to create a slightly irregular octagon. Cut along these lines to create such an octagon. Using superglue, secure this template to the centre of your CD, remembering not to put glue where the hole will be, accidentally gluing it to your work surface!
Next cut some strips of plasticard. The height of the walls is 1 9/16" (40mm), which is sufficient to give plenty of headroom for Guardsmen. If you intend these bunkerettes for Space Marines, you may want to add some height. Cut the strips to those dimensions. I used 2mm thick plasticard for this step, and for each bunker made three walls of 1" (25mm) by 1 9/16" (40mm) by 4mm thickness. Using superglue, secure these three to three of the short sides of the octagon. I propped mine up with bits of Lego, wood and so on. Do not worry if they are not perfectly straight. To err is human.
Next I used 0.5mm thick plasticard, and cut strips to fit between the two long sides which join the three short sides together. Laminate these to create thicker walls, if you are using such thin plasticard. Once you have done this the structure is mostly complete. The front part of the bunkerette does need a vision slit so your models within can plausibly fire out at the villainous foe. I took the 40mm tall piece of 0.5mm thick plasticard, and left 14mm at the bottom, 10mm at the top, and found this allowed Lascannon and Autocannon to poke out nosily. For the two pieces that touch existing walls, and are on long sides, I also left a 10mm piece at one side, so the plasticard shape resembled a C (or a ]). The one remaining short side I created from a 14mm strip at the bottom and a 10mm strip at the top. I secured these to the 0.5mm long side-Cs with some strips 0.25mm plasticard, and then laminated all of theseto a reasonable thickness.
Next I got out the old Greenstuff and filled in all the cracks and crevices that would muck up the look of the model. That done, by trial and error I carved the roof. The roof is of two parts, both of 2mm plasticard. One sits atop the structure. I got this shape by inverting the bunkerette, and tracing around it. Then there is an inner piece of plasticard, one which fits within the lip of the building. Glue these two together, and it has the look of an inverted step when upside down. I added a round brass hook (which I shall paint as comms equipment) to make it easier to remove the top of the bunkerette. Add yourself a door at the back, and a control panel so folks can get in and out, and Bob's your uncle! If anything is unclear, these pictures should render it pellucid. If it remains murky, just drop me a line and I'll do my best to clear up any misconceptions! Happy wargaming, folks!