Hello Mr G,
Commiserations on the roof fitting. Heather, Tony, you and I have had the same outcome, and is why I haven't finished the BG thread.
The roof sits down perfectly without the interior but, despite gentle filing down of the tops of the interior sides and guards compartment, it will not sit down with the interior in place. I have not been able to find the reason that this is so.
I considered finishing the vehicle without the interior in place but that would be a shame as it is so detailed.
Heather and Tonys' problems seemed to be due to a bowed roof, yours and mine don't so unless the tabs line up with the slots, with the interior in place, the bolts will just take the roof down to the top of the tabs.
Your idea of gluing the roof on gave me an idea though. If I deconstructed the interior and trial fitted each bit with the roof on before continuing I might find out before final attachment of the roof. Not sure about this yet, comments gratefully welcome.
I had the same thing with the corner becoming unsoldered, thankfully before painting. Necassarily, on the BG with rounded corners the joint is very thin, and the interior doesn't allow a solder fillet inside.
I'm looking forward to the tank wagons.
Ken