After Slorm's comment about the paper buildings on my previous post, I thought it might be useful to someone in need of some urban terrain done quickly and quite cheaply. It might be useful as an activity for kids, too.
Everything starts with a template. The idea is to build a box with five sides. You want to have some tabs on the open side to help keeping the building walls straight -- especially if you're using common scratch paper like me. The template is simple enough to draw by hand with ruler and squares but if you want to make several buildings, it may be worth to print the template (I have a couple at the end of this post.)
In my case what I do is to print just the outlines in "fast economy" mode and draw the details. Alternatives include drawing some basic outlines like doors and windows on the template before printing, maybe even some rough coloring (be sure to use some "economy" mode or you'll miss the point of keeping these cheap) or printing in colored paper.
My process is really basic: sketch with pencil, cover with a black marker pen. I have found that this works pretty well to create run-down neighborhoods, abandoned buildings etc. for zombies and dystopian sci-fi. The precariousness of the models fits the mood. So I draw windows covered with boards, broken doors, bullet marks, stains and spray tags.
Since the template is very basic, it can be cut with a pair of scissors instead of a hobby knife, if you want to. I suppose giving these templates for kids to create their own buildings might work -- either pre-cut or under the supervision of an adult if using scissors, obviously.
With the model cut, it's a matter of gluing the square flaps to the insides of the walls forming a box. Leave the long narrow tabs unglued and just fold them inwards to keep the walls straight.
Here's a view of the building upside-down, showing the folded tabs. I'ts possible to build structures of slightly different sizes and store them one inside another. I got this idea from Tommygun on the Cardboard Warriors forum
I'm currently in the process of making some better-looking, flat-folding versions of these for 15mm games (the details can be found here). Anyway, to finish this post, here are the templates for 16cm x 9cm and 14cm x 8cm buildings, printable in A4 sheets.