I'm not sure I've got the skill set to get what I want out of sketch up and other application to be honest and even if I did I'm concerned that it would take far too long to create the design.
Ideally I'd like to be about to draw a room/warehouse layout in 2D then plot mezzanine floor components in 2D (adding in the finished floor height etc) and it then creates a 3D image based on preset information.
I have seen this done with a piece of software from Multisuite but don't want to spend 4k on software!