The other way to look at it is that depending on the building you work out what the prototype would likely to be ... a garden shed or cottage might have a six foot stud whereas houses may have a minimum stud of eight feet .... commercial buildings much greater. Then you need to allow extra for the floor between each storey.
You then multiply the stud height [ floor to ceiling ] by the scale. I am not sure what the scale for 'G' is ... [1/20.3 ? which is 15mm/foot.] But if you are running American I think that is 1:29 or 10.5mm/foot. Awhile back I was modelling 1/24 or 'half-inch' with 45mm track representing the New Zealand 3'6'' gauge .... so I am going to be in a right pickle one day with various stock let alone buildings
If you run Gauge One, mainline UK prototypes on 45mm track, that is another scale.
With Brian's door at 86mm which would in most cases be a 6"6" door you have a 13.87mm/foot scale so what Piko is representing I do not know