System of enemy creeps atacking player bases.

[Aldeia]

Hello Guys, so, the thing is i need an custom survival system, i have a melee map, where players build bases , i need a system that will generate units on map, ( or regions) and will atack players bases.(players can be from 1 to 8).
can someone help me please, also i will add it to credits to my map.

 

[Wietlol]

Every ... seconds of gametime, create x units for player 9,10,11,12 and order them to attack a random building from 1,2 3,4 5,6 7,8 (one creep player for each 2 normal players)