if u used a multi-manager to spawn the zombies and then to trigger a scripted sequence once they spawned and make the zombies move in the disiered direction (an assuming that monsters from a monster_maker can be named and that u know how to use scriped_sequence)
the platform isn't a model by the way as the textures are in the hl.wad its just 2 bsp brushes one up and one down and it flicks between the two with an env_render
mp mapping isn't nub, if any thing its harder especily when u try to work out the basic lay out- because if u have to think bout the map from different angles ie where all the players spawns are all the possible routes and places to go-