The section will give some examples for common features of a DOOM level and show how to construct them.
Rooms:
A room can be the simplest structure in a DOOM level. Any sector can be a room. Create a sector and set it's floor and ceiling heights. A room can be any shape and have any number of walls.
 
Corridors:
There is really no difference between a room and a corridor. Corridors tend to be narrow and rectangular, although they can be any shape you want. Where the corridor meets a room (or another corridor), the middle textures on both sides of the common linedef should be transparent (type a single minus sign "-" for a transparent texture).
 
Platforms and Pits:
To create a raised platform in the middle of a room, or against a wall:
(1) Draw the outline of the platform inside the room.
(2) Make it into a separate sector by control-clicking inside the outline you just drew.
 
(3) Set the floor height of the platform sector to be greater than the floor height of the room.
(4) If you wish, change the lower textures of the outward-facing sidedefs around the platform to change the appearance of the pedestal.
The height difference between the room floor and the platform floor must be 24 or less if you wish the player to be able to climb onto the platform.
Pits are made in a similar way, except the floor height should be set lower than the room floor. To change the appearance of the interior walls of the pit, change the lower textures of the inward-facing sidedefs.
Make the pit deeper than 24 units if you don't want the player to be able to climb out. (Note: it is generally considered bad level design to trap the player in a pit, unless there is some way out, or the pit contains acid/lava that will eventally kill the player).
Windows:
To create a window between two sectors, first create a small "window" sector between the two. Set the floor height higher than either floor (32 units greater than the highest floor is suitable), and the ceiling height lower than either ceiling.
 
Pillars/Columns:
A pillar or a column within a room is normally created by making a 'hole' in a sector; i.e. an area of non-sector space within the sector. This is easily done by following these steps:
(1) Draw the outline of the pillar within the room sector.
(2) Make it into a separate sector by control-clicking inside the pillar.
(3) Select the pillar sector with an option-click. This will select the pillar but not the vertices of it's surrounding linedefs.
(4) Delete the pillar sector with the CLEAR (or control-Delete) key.
 
The hole that you are left with will appear as a pillar that extends from the floor to the ceiling.
Stairs:
Stairs are created with a sequence of small sectors. Firstly, divide the sector for the stairs into a number of smaller sectors (you will need at approximately (stairs height divided by 24) small sectors or more). Now set the floor and ceiling heights to even increments between the bottom and top of the stairs. The difference in the floor height between adjacent steps should be 24 units or less, otherwise they will be unclimbable. If you want monsters to be able to use the stairs, you should probably make the step heights smaller.
 
For example, say you need a staircase between a room with a floor height of 100 and one with a floor height of 200. Create a corridor between the two rooms. Now divide the corridor into four smaller sectors along its length. Set the floor heights of the small sectors to 120, 140, 160 and 180, starting at the sector closest to the lower room. Similarly, set the ceiling heights.
You can use a step-like (e.g. STEP1) texture on the lower texture of the stair risers, if you wish.
An important point is that the clearance between the highest floor and lowest ceiling of adjacent steps must be at least the height of the player (56 units), or the stairs will become impassible. It is probably safer to use a greater clearance.
