Where are you buying them? If you are referring to the S9s on Giga-Watts miner purchase site:
https://www.gigawatt.sg/shop/bitcoin-miner/antminer-s9-14-0-th-s-psu-included-batch-7-june/

Then at current prices and difficulty it would take between 220 days and 226 days to ROI at Giga-Watt, assuming you do not have to rent WTT.

That's a relatively long time to ROI, and given that the difficulty usually goes up, and with the behavior of BTC prices lately, it's not really a good deal, unless you have a sizable investment in BTC miners already and need to keep it going.

Then if you add in the usual Giga-Watt delays, it gets even worse.

I purchased WTT in batch 1 and bought a L3+ for mid-September 2017 delivery. The miner arrived on time, but due to the delays at the Giga-Watt facility, it didn't come online until 22-December. It was more than 3 months late coming online. When I figured the ROI in September it looked like between 60 and 75 days (LTC price was moving around a bit and difficulty was climbing). That miner still has not reached ROI, and probably will not for a few more months, depending primarily on the price of LTC since network difficulty is rising. It's currently earning ~4.42USD per day (5-May-2018 2157hrs US East Coast Time)