few questions before i start

i plan on doing a 30 plant grow with six 600watt hps lights. should i be using the 600watt lights during veg and flowering? and how much should i be expecting my electric bill, with out the grow room this building has nothing else using power, no tv stove ect... ill have some fans and water pumps.

For the first run you can but if you want a perpetual harvest and those are all the lights you have,I would use fluorescent lights for a veg and clone room,and those 600s for flowering,don't get me wrong hid are better overall for veg and flower but fluorescents are a cheap alternative for a veg room and you will still achieve great results.