I'm assuming you're talking about the buildings. They look like basic foamcore board walls and floors with balsa wood "supports", meaning that it looks like he/she used thin balsa wood pieces that were glued to the outside of the buildings to make it look like it's a wood framed building. Then they used spackle (or filler depending on where you're from) on the foamcore walls to give it a textured/stucco look.
If you're talking about the tiled flooring that makes up the ground, its most likely high density insulation foam that has the tiles/pavers/cobblestone hand carved into it. Very time consuming but can end with a great and durable look.
Hope that answers some questions.