(Here I am making an assumption that air resistance is negligible and that the height of the building is negligible compared to the radius of the Earth)
Using SUVAT equations,
v=u+at
where v is the velocity of the object as a function of time, u is the initial velocity at t=0, a is the acceleration of the object, and t is any instant of time. As the object is dropped from a building, the horizontal component of its velocity will always remain 0, i.e. vx=0, hence the vertical component will equal the velocity of the object, i.e. vx=v; also, as it is dropped from a building, the vertical component of its initial velocity is 0, i.e. uy=0.
As it is dropped from the building, the resultant force acting on the object is only the gravitational force acting on it due to Earth's gravitational field. The acceleration a of the object is hence equal to acceleration due to gravity g,≈9.81ms−2
Therefore, v=vy=uy+gt≈0+9.81t
v≈9.81t
Depending on the direction you choose, v and g can be positive or negative