I've been thinking about one made out of a coffee can. I would only use it for knives so it wouldn't have to be huge. Here are a couple of links I like.
http://www.zoellerforge.com/coffee.html
http://www.paragoncode.com/shop/micro_forge/
You could use propane, Bernzomatic or Mapp. I happen to have a Mapp bottle. I just need to invest in some new tips.
If you wanted to make it larger you could use a paint can or even some can larger than that and just apply the same principle.
Just some thoughts if you are getting started like me.