Floor plans, Sims mockups, iso/voxel renderings, whatever. Doesn't need to be at any particular scale as long as the scale is indicated in the design. One floor tile = one Trace/person standing. Will need at least one for each unique environment (anything separated from others by some kind of transition, including stairs/elevators).
Doors, walls, and general furniture are essential. Ideally, interactive elements should be included. Bonus points for including details like lighting and where NPCs will be placed.
Batbro
commented
7 years ago 
Sample floorplan
Floor plans, Sims mockups, iso/voxel renderings, whatever. Doesn't need to be at any particular scale as long as the scale is indicated in the design. One floor tile = one Trace/person standing. Will need at least one for each unique environment (anything separated from others by some kind of transition, including stairs/elevators).
Doors, walls, and general furniture are essential. Ideally, interactive elements should be included. Bonus points for including details like lighting and where NPCs will be placed.