Sheet steel is lighter than cast iron but doesn't have the ability to spread the heat as well, it is quicker to heat a sheet metal unit but it won't carry a consistent temperature, it also cools quicker. Might also mension that both will make it very hot below in anything but cold weather. I'm not sure how they would compare with fuel volume requirements and I would guess that there are good and bad models available in both cast iron and sheet metal. It might be a nice nostagic touch but I'm not sure how practical your idea is on a daily basis for cooking/heating but I'm on LPG and no heating as I chase the warmer climate. I wait for my morning coffee as it is
Peter 'coffee mug in hand!!'