Spanish buildings - roof?

Question:many houses in spain have a roof with exposed timber beams inside, covered with what looks like flat terracotta tiles. but on the outside the tiles are those traditional curved spanish ones. are the spanish ones flat on the bottom?! or is there something in between?!

Answers:
these are flat terracotta blocks ..sometimes they fix flat boards ..then cover them with the blocks ..then they concrete the roof ..locking all the blocks in position ..then they tile on top of the concrete ..when they take away the supports and the flat boards ..then when you look up you see a nice flat terracotta effect