What you need
I had 0.8 mm birch plywood panels sawed at the DIY store, and used some remnants for partition walls.Each floor is:
27.5" L x 15.7" D x 15.7" H /
70 cm L x 40 cm D x 40 cm H
For the back walls, floors and roof:
27.5" L x 15.7" H /
70 cm L x 40 cm H
For the side walls:
15.7" L x 15.7" H /
40 cm L x 40 cm H
For the partition walls:
8.3" L x 15.7" H /
21 cm L x 40 cm H
Caution! A three-floor house like ours is pretty HUGE:
27.5" L x 15.7" D x 48.4" H /
70 cm L x 40 cm D x 123 cm H