Thank you for your answer.
In regards to lining up the walls, I made sure the walls in Maya were lining up in the grids and the coordinate systems set to centimeters.
As for the back faces, I agree but my level is only one apartment and it’s an archviz project so I am not too concerned with the performance. Also the walls two “sideness” makes my work easy but if that’s the cause I will remove them.
So if I cannot get a smooth wall with multiple lining up, that would make the level designing or prototyping work time consuming.