If you feel like making your own, the general rule of thumb is, within the limits of what will fit in the connectors, thicker is better. Sure, there are they mystics that will go on about ultra-performance shielding and 99.995% pure silver conductors and whatnot; but, assuming your cables aren't being run in a horribly high EMI environment, your best bet is probably to just buy a bunch of basic two strand power cord(the ordinary stuff used on ungrounded appliances) and drop the appropriate connectors onto the ends(if any, your speakers may well just use spring clips). Such cord isn't perfect; but it is quite good for the money. In all odds, though, unless you are planning some rather long cable runs, don't bother.