My Butt don't have the cuff at the bottom, if I get a bbl done could it give me the cuff I need?

Ideal candidates are at a stable weight,  in good health , and have excess fat in some parts of the body and too little in other regions.  Gaining weight before the procedure is to no advantage and when you lose weight again the fat cells will shrink just like the donor site fat cells.  Typically, the transferred fat results in a significant increase in volume of the body site being treated.

Sometimes fat transfer can be appropriate.  Sometimes liposuction of the posterior thigh can be appropriate.  

It would help for us to see some photos of your butt and also a wish photo with the "cuff" that you are referring to.