Well, assuming you also had free BTC ASICs. Ensuring that your mining equipment pays for itself over its lifetime is an additional concern.
If I had free electricity, the only thing I'd change about my setup is that I'd consider finding an appropriate CPU coin for use with my existing rig.
And by the way, can a PC be bought and set up to do the job? What hardware should it have?
Not too long ago (great timing -just in time for summer ), I reassembled my old LTC mining rig of low-mid range 7700 & 7800 series cards and have them mining Zcash. Power is relatively cheap where I live, but it's not super profitable. I don't personally want to buy new cards for mining (especially with the current mining craze), but since I have them on hand and they have already paid for themselves, I'm putting them back to work.