For simples elevators, you must simply make a sector between two sectors
of differents altitudes.
This sector must have a lotag number (key [H]):
16 for a plateform wich start up
17 for a plateform wich start down
18 for an elevator wich start up
19 for an elevator wich start down
For others elevators, you must create two sectors strictly identics, but at differents altitudes, and at différents places. Put on each of them a S of value (x!17) where x is the number of the elevator, the sectors must have différents valus: [0;15]for the bottom sector and [1;15] for the upper sector, to finish, the S of the sector where you want the elevator start at the biginning of the level must be darkest than the other.
(To make two sectors strictly identics, you must align
them too the bigest grid of the map, in 2D mode, and align the floor and
the cell with the texture of the wall.)