Even assuming that you have free electricity and even cards, if you have to buy the rest of the mining rig at not a very good rate, that's a bad idea. Tell us at which price you can get a whole system and we'll then tell you if that's a good idea or not.
For the ZEC mining, it will take several years to ROI if you have to pay for the rigs and even if your electricity price is low.
With the current price Zec is trading at the moment it must be a win win situation for every miners at the moment and with the a good mining rig you could mine simultaneous coins and can double your profit, the only thing you have to worry is your electricity bill and the amount of noise and sound the rig produces.
