Its rather easy to do.....
a very simple room would be like so...
Click the cube icon,
drag the mouse in the window till you get the size shape you want,
while the cube is selected, go to MENU->Build->Convert to Mesh,
then select the Point edit icon and wire frame veiw,
Click the face select tool, and select the face of the cube closest to you, and delete it.
go back to the reguare veiw, and there you have a simple room shell.
to add a door/windows, go back into the point edit, and wire frame view.
view your object from the left, and then select the Cut Faces tool,
drag the line from before the top of the room, to just after the bottom,
make two vertical lines, you want to make them the width of the door/window,
then make a horizontal line 1/4 of the way up from the center of the cube all the way across the two lines you just made,
next click the face select icon, and select the face between the lines you just made, it should resemble a doorway.
to make a window do the same thing, only make two horizontal lines insted of one.
it should look like mine here....
