Hmm…
Just saw the pic on the side and immediately thought: a stack of Tupperware.
Stick on some puffy stickers or googly eyes for windows and paint.
Kmart has loads of cheap stackable containers. Or just reuse whatever regular food containers you buy. Such as Chinese or dip and yoghurt pots.
You could go crazy high.
Make them separately, then stick some to bases with small square entrances, like tiktak containers, match boxes or such. And some others with top gubbins like bottle caps and glue, drink, sauce, bottle tops, for roofs.
Then just stack as you feel on the day. Lots of low buildings, several high-rises, or a mix of both!
