"First create a cube and position it on the far corner of the ground plane grid. Stretch it along the Z axis until it just disappears off the screen at the left. Now stretch it along the Y axis to a position as shown... "

That's how the tutorial begins... but even at this early stage, if I look at the Nano preview window... it's clear that the cube is hovering. In his screenshots, he's got the cube squashed flat at the very outside edges of the working window (on the farmost lines of the ground plane grid)... but his are not hovering... yet mine are...

I tried the get rid of the shear and then use the down arrow to land my wall... and it does land... but it "jumps" quite a bit forward into the center of the canvas when it lands...

Sorry... I'm not usually this much trouble... honest! ;)

I guess maybe I could try to go ahead and build the room with a little less depth than he shows in the tutorial...

As I mentioned.. I can get the boolean window opening with no trouble... and the lights... but because my walls are off the floor so much, the shadows are all jumbled up in the room and it's just not the ticket....

Thanks again for all your help, Roch222.... :)