The stretch marks tend to be something that are more likely with rapid weight gain.  That I guess could happen with steroids if you had had a period of overtreatment.  I note that my son is very different build to all the other children.  They are all slim and well proportioned and he is somewhat smaller and easily gains weight.  He has had a more leaner physique but he was undertreated somewhat after a few months of looking like that, and his doses were put up. 

Taking the med alters your whole metabolism, stature and finally your weight if over treated, and the same if undertreated.   In adulthood, I’d imagine you can better determine your dose so that your weight is not too much for your height.  Well I was hoping that this would be the case anyway.  :)  Whereas in childhood, the concern is more with growth in height and trying to balance that with as near to normal bone age for chronological age.  The weight can be an indicator of over treatment I have found over the past few years and is worth having your Doctor take a look at.