Materials you need are:
a set of steps (to run up)
a set of measuring scales
a friend (to time how fast you run up the steps)
First, find out your mass in kilograms. Multiply this by 9.8 m/s2 to get your weight in newtons.
Second, measure the vertical height of the steps that you will run up.
Third, time how long it takes you to run up the steps.
Last, use these rules to work out your power in watts:
Force of Gravity (Weight) in newtons = Mass in kilograms × 9.8 m/s2
Work done in joules = Weight in newtons × Vertical Height of Steps in metres
Power in watts = Work done in joules / Time in seconds