i have one in my shop that i built out of 2" thick oil refinery type of pipes.
you have to start it off on wood, when you get it down to coals you can turn the oil drip on.
the thing gets super hot -- they do make plenty of heat cheap but they can be fire hazard as hot as mine can get. not something to be left unattended at all.
since the economy turned to shit i don't have near as much used oil to burn as i did. it is mostly a wood burner these days.