I will use something like that
draw closed surfaces (rectangles, polylines etc...
Trim each closed lines
Planar each closed lines for make each surface
Each surround surface with a name + color
Will be more easy as soon as project has more than 2 pieces! :)



then Flat Lines by Max Smirnov https://moi3d.com/wiki/MaxScriptArchive
Extrude
all walls are solid and can will be Booleaned...and very easy to snap at the good hight...
And calculate surace a game boy! ;)
In fact you can recreate SketchUp inside Moi3D! ;)