since you are new to mining
i suggest you should not go 12 cards mining rig
first buy cheap used PC with good high wattage power supply ( 750w minimum )
buy 2x used cards ( 1x nvidia & 1x amd )
then put your hands on building it and do some mining and learn how to manage it

then do the calculation on this PC in term of profitability and electricity

after that you decide if it is worth it or no