The burj khalifa in dubai is the worlds tallest building. it rises to an amazing 828m above the ground and if you were to get to the top using the stairs, you would climb a total of 3234 steps!
if each of these steps has a depth of 20cm, calculate the total work done by a man of weight 800n who climbs to the top of the stairs?

I don't understand what you mean by "depth" of the steps.  The flat part of the step has a front-to-back dimension, and the 'riser' has a height.  I don't care about the horizontal dimension of the step because it doesn't add anything to the climber's potential energy.  And if the riser of each step is 20cm high, then 3,234 of them only take him (3,234 x 0.2) = 646.8 meters up off the ground.  So something is definitely fishy about the steps.

Fortunately, we don't need to worry at all about the steps in order to derive a first approximation to the answer ... one that's certainly good enough for high school Physics.

In order to lift his bulk 828 meters from the street to the top of the Burj, the climber has to provide a force of 800 newtons, and maintain it through a distance of 828 meters.  The work [s]he does is (force) x (distance) = 662,400 joules.