The first step is to calculate the area of the roof (in meters). This will be:

Now, we can multiply this by the solar radiation, which will give us:

However, we must remember that W is equal to J/s. So, we can find out how many Joules there are by multiplying the Energy and the time:

Note that we needed to multiply it by 3600, as our time needs to be in seconds, not in hours.
Then, our final energy is E=305415185J