Exterior wall above roof

[Rapearson]

Hi, guys, I am working on a small project but I am stump on a little issue which I know should be a  simple fix. I can't seem to get my walls above my flat roof to be exterior walls with sidings. Can I get someone to point me to the reason and the solution? here is the file if someone wants to have a look. NB All other advice or if there are any other flaws in my project that anyone viewing my notice and want to point out are welcome as I am still finding my way around chief. 

1007_ASHY_GROVE_NEW.plan