I'd been telling my boys for a long time that I'd make some different blocks for them. I ended up making planks instead. Like lumber they are pretty easy to stack and arrange. The basic module is pretty simple. The pine board I made them from was 3/4" (~19mm) thick. I ripped it down into strips so that 3 of the strips stacked together would be as thick as the board. Then I cut that into a few different lengths. Most are 15/4 of an inch long, some are 18/4, others are 30, 45 and 75 quarters.
I used plain white pine. It is cheap and light. If you are going to do this yourself make sure you search through the boards and find one with vertical grain - the growth rings perpendicular to the width of the board - for the best results. I got about 300 pieces from a 3/4" x 12" x 6' board. Spruce would be a good alternative to pine.
The results are reminiscent of Kiyomizudera: