i am having trouble with building levels in russian

я поднимаюсь на вершина здания - i am ascending to the top of building.
how do i say 'i am ascending to the top floor'?

я поднимаюсь на верхний етаж - i am ascending to the upper floor?
did i say that right in russian?

я поднимаюсь на третий етаж - i am ascending to the third floor.
do i have the correct preposition here?

я спускаюсь в низ здания - i am descending to the bottom of building
how do i say 'i am descending to the bottom floor'?

я спускаюсь в нижний етаж - i am descending to the lower floor
did i say that right in russian?

я спускаюсь в третий етаж - i am descending to the third floor.
do i have the correct preposition here?