building an open shower

[simon benn]

Excuse the lack of expertise - I'm a plumbing virgin!
I'm currently building an open shower in the corner of a largish bathroom. The floor is concrete on brick supported by reinforced concrete beams above a cellar (this is in Spain by the way) I plan to make the floor to a fall using cement sealed with 'gaucho' - a thick paint-on rubber membrane. This will then be tiled probably with small tiles on mesh. My question is what type of trap is best for this and how is it best fitted?

Have you ever thought about using free formed backer board. Perfect for your situation.