OK I'm a 3DSmax n00b but I thought I'd give an explanation of the way I do it...
I' m sure other people do it lots of different (Probably better) ways..
Ok start by makeing a box. In my example it's 20m x 20m x3m convert it to poly. Make sure your snap is set to 10 which is 1m.
OK now change the snap to 2, Change to the polygon tab select the bottom polygon make some quickslices for the outer walls at .2m from the edge
Select the polygon in the middle extrude it -29.
OK select editablepoly and make some slices for the door in my example it's
1.2m X 2m
select the polygon at the bottom for the door and extrude it -20
select and remove the unwanted polygons from the door use Backspace not delete.
OK now do the same thing for the windows in my example there 2m wide.
Go to polygon tab select the two polygons as you see. And make a quickslice maybe 1m up then extrude them 2m.
Now for the internal walls . Ok start by going into the edge tab and select the unwanted edges and remove them with backspace.
Ok now select the polygon for the inner ceiling, and make slices for the internal walls then select the polygons you want and extrude by 29.
I could go on but thats about it, make the internal doors the same way as the outer one. Obviously this needs a lot more detail in the windows and doors and stuff.