Question

a part of a room or building which forms the lower enclosing the part you walk on

Answer 1

a part of a room or building which forms the lower enclosing the part you walk on is floor

Answer 2

This part of the building is the floor.  

It is the bottom surface of the room.

Floors usually have a subfloor for support and weight bearing and a floor covering such as cement and tiles to give an excellent walking surface.

In modern buildings, the subfloor often has electrical wiring, plumbing, and other services built in.

As floors must meet many needs, some essential to safety, stories are made to strict building codes in some regions.