Inside your main() function, under zm_usermap::main();, add:
// cumulatively add this to the zombies' starting health each round (up to round 10)
zombie_utility::set_zombie_var( "zombie_health_increase", 100, false, column );
// after round 10 multiply the zombies' starting health by this amount
zombie_utility::set_zombie_var( "zombie_health_increase_multiplier",0.1, true, column );
// starting health of a zombie at round 1
zombie_utility::set_zombie_var( "zombie_health_start", 150, false, column );
Variable
Explanation
zombie_health_start
Health of zombies on round 1
zombie_health_increase
Amount of health to increase by each round until round 10