I can now update on this subject. In the last entry, I placed several photos and will repeat one, namely, the shed in the wrong place

In the end, I decided to chop the shed down to its original height by removing the supplements I added several years ago. The photo also shows the door posts I had to remove. When I relaid all the track early last year to improve the dcc feeds I did not take into account the track centre-to-centre distances nor was I too careful in seeing that the straight sections were really straight. This meant that the shed entrance was not wide enough and the locomotives were either colliding with the posts or rubbing against them, contrary to what I said in the previous post. I first removed 2 mms from each side, which was fairly easy since it meant slicing through 4 layers of glued card, but when I placed the shed on the new floor, the entrance was still too narrow. This now meant slicing through 6 layers of glued card and this was just too much so I removed the whole post on each side and made new narrower ones from balsa wood, covered with brick paper. When I placed the remodeled shed on the floor I found it was off-centre relative to the tracks, i.e. the locomotive went in with a large clearance on the north side and was rubbing on the south side. This meant slicing 2 mm off the north side of the floor and adding them to the south side, which finally settled things more or less satisfactorily.
Finally, like mentioned in another post some days back by another contributor, I do not want the shed to be a permanent fixture and since the floor was made practically to the same dimensions as the shed's footprint, I added a skirt to each side which fits down the side of the floor, preventing the shed from being accidentally displaced but making it easy to lift off as and when required.
I now have the problem of making a signal box which does appear on the original track plan compatible with a water tower which does not, because the available space is limited and the tower could limit the view of the yard from the box.
Finally the installation of an additional platform as mentioned last time will require a serious rethink.

A front view of shed.

Side view with skirt

Pieces removed