Do you require your Lego structures to be fully connected? Seems like that limits the possibilities a bit, but it would mean you can safely pick them up and move them around, which is always fiddly in normal Zendo.

We don't require it but inevitably people build fully connected structures due to the ease of pickup and move around.

Wow, Lego blocks! That's a great idea, I'll have to try it.

They key thing when using Lego is not to go crazy with variety you need a large number of a small variety of blocks.

Makes sense. The one meta-rule I always emphasize when introducing people to Zendo is "make the rule really simple, it'll be much harder to guess than you expect."