Heating block built shed

Paraffin heaters produce roughly the same amount of water as they burn in fuel.
i.e. burn one litre of fuel and release 1 litre of water in the form of water vapour.
Do you have sufficient ventilation?

You could try this type of diesel heater, as used in buses and caravans.
Make sure you vent outside.
There's a guy on youtube who has done a strip down review, which was favourable
amazon.co.uk/Tri…DHD

Whats the purpose of the heating?

Do you have a decent source for the paraffin? That would be my stumbling block. Diesel can be had anywhere, and I think I could source red diesel easier than paraffin (although I think this has changed recently and red diesel is no longer allowed to be used for heating, could be wrong)

Have you looked at the Mr heater big buddy. Might be worth considering. It's gas though

Paraffin heating is widespread in the UK. I'd imagine paraffin/kerosene is the most common boiler fuel for properties that don't have access to mains gas - you certainly see plenty of garden tanks for it in villages and rural areas.

Is that the sort of setup you're looking at, or are you considering something cheaper like an outdoor or greenhouse heater?

I'd be cautious about anything unvented that was exhausting the combustion byproducts directly into the shed. Depending on how often you use the building it may be acceptable, but if you're using it every day then it's not something I'd consider.