Zzulu.
Those are Gork & Mork.
I doubt very much Warbosses can grow to the sizes of gods.

Why not. I bet there are mountain sized ork monstrosities deep in the ork systems where no man has gone for thousands of years. Only our imagination is the limit

I would guess that Warbosses are typically around 10-15 feet just from what I've seen in artwork and games. From my understanding, Orks only continue to grow if they are especially successful in combat. So for a Warboss to grow even larger than normal he would have to remain undefeated against other Warbosses, non-Ork armies, etc. Essentially, in-fighting between different Warbosses would regulate their size except for special cases like Ghazghkull or The Beast who united many tribes together.

thats a bad idea id say for every 100 kills or 10 thousad damage points taken they grow a bit and its perminant wich would encorage orks to charge out of corse kills would have to be worth more growth points

there would have to be a max hight for each class or warboss

Double the size of marines for warboss, triple for a warlord with a funny title.

Some where i say it that Thraka was around 24ft in height and 19ft wide at the shoulders thats with out the armor

Thraka was a unique case among Ork kind but then again you must remember that even in the close of the millennium, he is considered a threat that MUST be hunted down and destroyed, a rare course of action in general for the Imperium that has become more of a defensive institution by and large.
Orks can and do get bigger and bigger with combat stimulii and I find the idea of a dreadnought sized ork warlord perfectly acceptable.

I agree with u and i was just putting numbers to his size to help the others out.

Ever seen Chimpanzees in the zoo? Chimpanzee's have this thing where when a young adult starts getting brave and ambitious he will begin to put on weight and muscle mass in preparation for challenging the current Alpha Male; should he fail his challenge he will being loosing weight and mass back down to the "base form" however if he defeats the Alpha and ascends to a position of leadership he will begin putting on additional mass and weight until he is the largest in his troupe.

Orks do the same thing so really the only limit to their size is if there is an Ork bigger than them; an Ork can only be as big as the biggest Ork there is making it theoretically without limitation. I recall reading in one of the Ork armies books about an empire just south of the Imperiums borders were massive Orks have been spotted even the standard Ork Boy there is as Large as the Nobz found inside Imperial Space.

Hopefully not too big unless there's a corresponding increase in health. Being huge means he's pretty hard to miss.