Sonali, the biscuit roulade is baked in a very thin layer, less than an inch, but it can be stacked several layers high. The genoise (ideally) bakes up into a thicker layer, 1.75” or so.
If you want biscuit in a layer cake form, use the biscuit de savoie. It has a less tender texture and more open crumb than genoise. And it does not have any butter flavor (the genoise does).
The same skills are used for both cakes, whipping eggs and folding. The biscuit has you separate eggs and whip the yolks and whites separately, while the genoise whips whole eggs, but has you fold in butter, which is heavy and perhaps more difficult to fold successfully. Personally, I find the genoise easier because you don’t have to mess with separate bowls for whites and yolks.