Aligning walls on different plane

[Timothy Leung]

I'm a newbie in ArchiCad coming from modelling in microstation and sketchup.

Currently I'm trying to model a roof that has a 'fold', changing angle along a diagonal line.

I've started off with 2 single plane roof but the tile finish does not seem to be aligning correctly.

Are there ways to adjust the reference line when drawing the roof to be along the top finish rather than the bottom?

or am I better off drawings the roof as a mesh ?