you have to look this way , 1 TH/s is 10000 H/s  so my gtx 980 ti that has cost 800 eur last year is making around 470 H/s it think 1080 will make litel more , but the point is you need 2 gpus that cost 1600 eur to make  1 GH/s = 1000 H/s the you need 20 gpus for 1 TH/s that will cost you 32k eur +- 2k (if you get discount) and you are still not br there what will you get from antminer , and there is the elect bill 2 gpus take around 300W * 20= 6000W .  that is if you will be farming Zcash whit that speed i dont now how much speed you will get on bitcoin newer testes whit my rig , but i think that it is not far away Gpu you cant compere whit antminers they are made only for that coins (bitcoin), if you get that speed in alt coins that other story then you will be making some money.