Irrlicht Engine

I am now doing my final year project which is to allow users to design a 3D floor plan.

My supervisor told me to give some floor plan templates for the user before letting them continue editing it. The easiest template must be a cube without the top.

But I am quite new to computer graphics and can just think of one way to make a cube without the top. The way is make 5 cube scene nodes and set their width, height, length accordingly to form different rectangles.

However, later I have to build more complicated templates for users, I think I need a terrain creator.

Anyone has suggestions?

I discover that copper cube can do what I want. (e.g. the copper room in the prefabs)
But I would like to know how to make my own room instead of using the room from copper cube (i.e. export the copper room into *.irrmesh)