ok I'll give it go but I think some people would have a better idea of this than me.
Firstly I think that fat starts off differently on men and women. This may be due to a higher percentage of men having more muscle than woman but I dont know.
So I think woman who are chubby and bordering on fat are around 190-200lbs while for men it's around 220-230lbs.
300lbs is the beginning of obesity the safe zone, a good compromise between wanting fat and staying healthy.
this is also the point where your body has filled out, everyone begins to take shape ( apple, pear ect...) when they start to gain and this is the point where the shapes been completed.
And now we get to the fun and interesting of becoming morbidly obese, after 300lbs is when fat goes wherever theres space: bellys start to really drop down, hips and butt become much wider than the rest of the body and breasts expand horizontally. this goes on until about 450lbs.
And after that? pretty much immobility, there isn't really any variations of body types except the two that I call the blob and the tank ( I'm sorry my naming sucks this is what came to mind
).
The blob is what you expect, an apple figure out of control not much to explain.
The tank is when more than half their weight has gone to the butt and legs and they just have two massive tree trunks that revolve around their lower body to move them.
Btw my experiences are mostly with women