My only hiccup during creation was that I assumed that wanting the base at (0,0,0) required moving the origin to the lowest extent of the shape. Of course that’s not something we have been shown, so it’s not how to do it. Subsequently I changed the periscope’s location and it’s golden.
VERY IMPORTANT POINT: When you do the next bit, it is possible to get the vertex count down to 8 by removing edges and rebuilding the faces, though the video only reduces the count to 12. IF LIKE ME YOU GET EXCITED AND REDUCE IT TO 8 YOU HAVE TO PUT SOME OF THE EDGES BACK TO DO THE NORMALS EXERCISES!!!