Lots of houses, not a 2x4 to be found

This pic was taken on top of our building looking down at the building they are constructing next door (just behind my bedroom wall, to be exact.) Trees are in short supply here, so it is EXTREMELY rare to see a wood frame building. I've seen plenty of building construction in this country, but always wondered how the roof was done. Not that you all may care, but I do and it's my blog and I'm posting it. Apparently they use these slabs and then just pour concrete in between them. Nice.