Help with creating a boot drive for hackintosh machine

Right hi! I have no idea around a mac, but I do know my way around a computer, use to windows. so please excuse me for being a noob in mac xD.

My parents have a hackingtosh that I built them a while back. I used a 120gb SSD for the boot drive and that's it.

They now need a bigger HDD, so I'm putting in a 500gb HDD, but I tried this a while ago and couldn't make a bootable hackintosh HDD. How do I go about doing this. Somehow I managed to do this, but the 500gb or 1tb HDD I have in there atm, cannot remember which. Only will show up as 120gb --- the same as the SSD. Thanks in advance