When you have the electricity cost covered by landlord, it makes sense for you to buy less efficient but cheaper (per GH/s) miners.

For comparison:
S3: $149 for 453 GH/s = $0.329 per GH/s
https://www.bitmaintech.com/productDetail.htm?pid=00020141015100808946Nj1LM03y0650

Batch 4 S5: $401 for 1155GH/s = $0.347 per GH/s (and you won't get your miner before January 12th)
https://www.bitmaintech.com/productDetail.htm?pid=000201412231604153619o9X1obn0693

SP20: $659 for 1700 GH/s = $0.388 per GH/s
http://www.spondoolies-tech.com/products/holiday-special-sp20-jackson-shipping-from-stock