Hi Leylia -- unfortunately I'm not a soapmaker myself, but at least I can try to 'bump this up' a bit in case some soapmakers have ideas about or experiences with making molds.
Of course I don't know what exactly you want to make... but, apparently at one time there used to be (maybe still is?) a kit you could buy to form your own mold over another object. Have no idea re cost, but you might try checking one of the fairly large chain crafts places such as Michael's, or maybe even Walmart's crafts section.
~~ I've noticed that 'metal' soap molds are sold -- usually plain straight-side tube shape, but some have the side bent into some appropriate shape, such as a star for example.
Depending on what you're trying to make... at a DIY home improvement store, for example, it's possible you could find some sort smooth/shiny finished, easily-shaped/sealed sheet metal to experiment with.
~~ Or, if you think you could cut up something flat & more-flexible, it occurs to me that you might be able to use some of those new flexible silicone baking sheets or hot pads. If you can find reasonably inexpensive ones, of course -- some seem outrageously expensive to me.
But anyway, most of the silicone kitchen items I've seen are heat resistant to at least 500 degrees, if that matters or helps any.
~~ Just guessing here but I'd say whatever material you use, one thing you'd need to be sure of is that the mold is leakproof/waterproof & smooth on the inside.
~~ Some ideas for other things to use besides strictly-soap molds & for making your own at this site:http://www.colebrothers.com/soap/molds.html
~~ And this one has pretty-detailed instructions for making, lining, using a simple basic mold out of wood; for a different shape, maybe you could adapt the plans or the general idea : http://www.chestnutfarms.com/Soap_and_supplies/info/mold_plan.html