A large heavy rock, a medium size stone and a small marble are dropped at the same time from the roof of a building. Neglecting air resistance, which object will strike the ground first?

They would all strike the ground at the same time. If air resistance is neglected for example in an airless tube, then gravity is the only force acting on them and it has the same effect on them dropping so the drop at the same speed.

I believe that they would all hit at the same time due to the force of gravity actuating on them. All things fall at the same speed I believe.