Hi @s7evin-kelevra.
This architectural modeling guidelines doc was published recently.
It lists floors thickness as “24 cm (12 cm along +Z and 12 cm along -Z)”
24 for Wall thickness as well.
~
I’m wondering why they used 12/24 instead of 16/32.
My first thought is that 32 would look too chunky… (seems negligible to me)
The standard height is 384, which is evenly divisible into 12/24
384/24 = 16
384/12 = 32
In the context of Heights, there is a lot of space between 256 and 512 - so thinking in terms of ratios instead of ‘power of 2 grids’ could be an approach.
Someone get a metaverse standards committee in here. 
I’ve been having fun creating with all the architectural pieces in UEFN, I look forward to Marketplace/Fab asset packs built with these standards in mind.