Get a Lic Spark in and he will do a Max Demand Calculation for the installation and install a mains cable from your existing meterbox on its own circuit to the shed the the size of the cable installed depends on many things 2 being are
1/ Max Demand of the Install ( the current drag your shed will use)
2/ The distance the shed is from the Meterbox to compensate for Volt drop)
As you can see by throwing in a conduit for the spark you might think you are doing him a favour but if you throw something in to small and the cble does not fit then what was the point of the exercise!!!<!-- / message -->