In my map Im incorporating the health increase to a certain point idea... Like in Test of Survival... you start off with about 1/4 of your total health and everything you use to heal only goes up to that, never any higher. Then when you finally kill a pylon... you get boosted to 2/4 of your total health. How do you do this?
Just add in heal trigger, player 8 suffers 0 deaths of pylon set player health to 1/4 when suffers 1 death of a pylon its 2/4 so on.
\\Moogle
And if that doesn't work there is a tutorial here
Tutorial!Basically you use the modify unit hit points action.
However, note that after you heal a zerg unit to a certain % they can stil regenerate health and therefore gain more than the % health they should have.
If you are using very high numbers such as up to 9999 health then the health regenerated is negligible. Also it helps if zerg units are not left idle for long period of time without getting attacked.