Build and Shoot

I would like to ask how they did it in aloha.pk Fallout server it say that five minutes elapsed and the players over the ground throwing grenades down the server.

I would like so:
-5 Minute be Grenade rain
-the water level of block 20
-do not throw a lot of time off (cause lag), ie 3 grenade/játékos
-and if you can Grenade when válltsa rain mist green (RGB: 0 0128)
-grenades damage!


Thanks for coders.