Ah yes, familiar problem. My solution was:
- use a solid colour for walls in sh3d preferences,
- screen-grab (Win: Alt-PrtSc) sh3d layout,
- paste and bucket fill correct colour with Paint, Gimp or whatever,
- do touch-up on windows/doors etc
Same concept, but ordinary paint tools may be simpler than a vector based one. And sh3d is still my favourite for doing the actual planning.
Good luck with your application. And wish me the same...
ok