I base all my 25-28 mm + figures on 25 mm square bases (and usually put figures hat come with 20 mm bases also on 25 mm bases)
I'm still using imperial measurements so I try to do 1 1/8" doorway width and corridors for "single figure" width whenever possible
when I can't, ends up being only 1" or 1 1/16"
I don't generally fudge when 2"+ corridors and rooms...the extra ~0.4 mm per inch generally works out to allow figures to fit
after starting with hand cut 1" bases many moons ago then decades of 25 mm, I don't even understand 30 mm + bases...'cause now 30 mm bases wouldn't even fit some of my (urban) terrain...
for height, doorways 1.75" and room height 2.5" (at scale this is exaggerated to ~12.5 feet...all things considered, probably a good compromise)
anything that doesn't fit requires a placeholder token or such
this fits most figures even with raised arms/weapons
in short, key horizontal off the bases width and height is a judgment call depending on your collection of figures
hope this helps...
good luck and pls post your progress