ArenaMapDoc.txt

How to make a map compatible with DRPGs arena system (rough, UDMF only).

Map marker:
You must have your Map Marker start out as DAMxx (e.g. DAM02) for organisation.
DAMxx = DRPG Arena Map + Number.

Monsters:
Instead of placing monster spawns, you must use Map Spots with a TID of 1100 between 1129. DRPG picks TIDs at random to spawn monsters at different spots. You can have duplicate TIDs placed.

Identifier:
You must place a Thing with an type of 31001. This allows DRPG to correctly identify the map as an arena.

Items:
I do not recommend placing many items around the map as the player will generally get something at the end of each wave and they also can resupply via skills/focusing and dropping ammo packs.  

Maps exits:
Use Exit_Normal. This will be automatically handled via DRPGs exit script.

Sectors:
Give all your sectors an ID of 100. This allows DRPG to modify said sectors for the Arenas mini events (Foggy, pitch black... etc).

Scripts:
Lastly you must have a means of activating the arena which requires calling two separate scripts.
The first script must be repeatable and ensures that all players are ready. I recommend having this as a crossable line or switch.
The second script must be repeatable and starts the arena. I recommend having this as a crossable line or switch.
The third script must be repeatable and allows the players to select the wave the wish to start on.
They must not be called both at once. Both means of activation must be separate. 

Optional, but I recommend placing key'd doors with pickups inside incase the player gets lucky and gets a key drop.

Below is ready to use ACS for your map.

#include "zcommon.acs"

// Enable/Disable the Arena
script 1 (void)
{
    ACS_NamedExecute("ToggleArena", 0);
}

// Passed the Arena line
script 2 (void)
{
    ACS_NamedExecute("PassArenaLine", 0);
}

// Select Arena Wave
script 3 (void)
{
    ACS_NamedExecute("SelectArenaWave", 0);
}