thanks, i've tried that too and although it improves the walls, the roof gets darker!
how can something so simple in priciple be so difficult (if not impossible) in practice?!
also, i recently saw some simple 2D (overhead) siteplans including some basic plant symbols and both the plant symbols and other objects (e.g. house) cast shadows. i think these were drawn in autocad but is it possible to cast shadows in floorplan mode in AC10?