Been done recently I think?

Depends what sort of workshop you got. If it'll hold any sort of heat use an oil-filled radiator. If you want quick heat that warms you and not the air use a radiant IR one. Don't be tempted to use any sort of flame type as petrol fumes are heavier than air. Ditto fan heaters that may spark.

I have a gas one in the workshop, but I do mostly wood butchery in there, the type that runs off a 15kg bottle. Heats the space up quickly and gives out a good amount of heat for the bottle used. Thats fine if you dont mind an open flame, worse that happens is that if I am cutting timber using the circular saw it flares a bit on the dust in the air.

There is a thread on this somewhere.

The other thing with gas heaters is the moisture and CO2 from the burning gas builds up very quickly and can be dangerous/cause massive condensation.