I've been fiddling with other ways to create flat-folding glueless models, inspired by TopoSolitario's great IKubes. The first picture shows the results of my experiments, including some 2"x2" blocks, a ramp and a wall.
There are two versions of the block. The most basic one is built from a single strip of paper, requiring nine cuts. It can be easily drawn with a ruler and square. The downside of this version is that some parts of the top stay raised, making the resulting model less appealing. The other version adds some tabs and slots to help closing the box. In both cases, the bottom of the block is open and a diagonal support can be inserted to add stability.
Two or more blocks may be connected using a short strip of paper, which acts like a simple clamp. This way, several blocks may be used to build larger structures. Blocks can also be stacked on top of each other to create buildings of different heights.
Here is a picture showing the unfolded models. From the top left, in clockwise order: the basic block, ramp, the alternate block and the wall (certainly the most complex of these structures.)
Even though I did these tests using common paper (75gsm) the results were reasonably sturdy. In the end, the modular blocks are less efficient than the IKubes -- I would need two sheets of paper to fill about the same volume as a single IKube. However, these blocks may be useful as an additional option for flat-folding, easy to build terrain.