I always thought something like an Antminer S1 might be more suitable for someone with free electricity. Reason being that you can buy used ones off eBay for very cheap. Here's one that was selling for $40 NZD (about $30 USD) on Trademe (basically our equivalent of eBay):
http://www.trademe.co.nz/computers/other/auction-862628667.htmAccording to
Coinwarz, 180GH/s at zero electricity cost should reach ROI in about 2 months assuming that the difficulty stays the same. After that, it's pure profit. Plus, you could sell the miner for virtually the same cost you bought it for and make even more money on top.
Modern miners like the S5 are much more efficient and are able to produce nearly 4 times the GH/s per watt compared to the S1 but they also cost much more to purchase. If your electricity is free, then it might be a better idea to go for the horribly inefficient miners that nobody else wants because they are currently cheap as chips.
I will also say to anybody that claims they have "free electricity" to check the realities of of their situation. Somebody is always paying for the electricity they use, but they think it's free" because they have paid for a "normal" amount for their apartment, dorm room, or parent's basement. The key work here is normal, or expected usage amount. Beside the expectation of whoever is paying for the electricity, you will need to look at the capacity of your electrical service. Student dorm room might have a couple of outlets, probably all on the same circuit. When I went to college, there were serious restriction on things like "hot plates", other high power devices. That wasn't just to annoy folks, it was because the place wasn't wired to support more than some lights, a couple of computers, and maybe a TV. I seriously doubt that college dorms are wired that much better today to support a killowatt or two of Bitcoin mining hardware.
Same thing, on a slightly different scale for your apartment or parent's basement.
Think twice about using your employer's space and electricity for mining. While some may be cool with a small amount of mining that doesn't disrupt things, other employer's have zero tolerance Bitcoin mining on their dime as it were.
Any situation that allows for a space heater should be enough to accommodate Bitcoin mining. A small space heater consumes over a kilowatt of energy. An Antminer S1 normally consumes 360 watts. The S5 consumes slightly over 500 watts. Instead of using the heater to heat your room, you could use a miner or two during those cold winter days and your overall electricity consumption should remain pretty much the same.