Electricity for warming your shed is pretty much ineffective, I know that myself. As warmth that is generated through electric energy is just a side effect, it isn't even really good for the devices you do it with (because electronics love warmth - exactly, no, they don't).
Or, if you have suitable devices to do that, then don't take a look onto your meter.
In fossil fuels is such a huge amount of energy, especially warmth, compressed and and concentrated - if you want to beat that with electricity, you're going to break a leg or get broke.
That's really a bad idea...

If for, if wanting to warm something like water, I don't know, hm, this may work easier. You heat it once and try to keep the heated water warm. Like in a water boiler if you want to make youself a cup of tea or a cup of cofee.
It doesn't necessarily have to eat away as constantly as heating does.