It would be awesome if the room modeling tools were expanded on to include the ability to create vert extrusion rooms with a non rectangular floor layout and a none flat ceiling..
thinks its time for the modeling section of agi to be overhauled and improved 10 fold.
The idea would be awesome, but I'd sincerely doubt it'll happen.
Lighting Analysts created the plugin for modelling from Sketchup, largely because of needs such as what you're discussing. If you haven't tried Sketchup, give it a go. It'll do what you're needing very easily.
What would be good would be enhancements to the plugin and other processes so that some of the rough edges in the translation from Sketchup Model to AGi32 object were easier to deal with.