Hi Eric. Have added a bit of info as requested. Want to do working drawings for builders, approval from relevant authorities (here in Australia that is Councils generally or certifiers). The parapet walls have a "boxed" gutter that is directly behind them so when the water runs down the roof it runs into the gutter(s) which in turn have rainheads (pipes from gutter down to ground level and then into the sites's stormwater system. Hope this helps a bit.