Floor tiles and pillars.
Each corner has a quarter of a (concrete) pillar, so if you put them next to each other you can easily create a hall with 1 asset filling 1 baseboard. Put some HUGE walls (like HUGE wall brick grey, kuid2:645812:97930:2) between the pillars to 'complete' the hall.
Floor will initially be 50m below the baseboard. To make it visible, either raise the asset or use digholes.