you can also read this in dutch:
Step 1: Get a metal container.
height about 50cm
diameter about 30 cm
depending on how big space you want to heat.
I have also tried various metal rubish-bins.
it doesn't matter if the metal is thin. that way it heats up the space much faster.
don't use anything aluminium. it will catch fire when tempreture gets high enough for spontanious combustion, melting or realy aggressive burning with hot sparks flying about.