Imo it isn't worth it to mine bitcoins in 2018 as the current electricity rates are very high (especially in India) and even Nvidia declared that they don't want to sell GPUs to miners but they want to sell them to gamers as they get feedback from them.

Keeping the hardware and electricity issues aside, the difficulty while mining has increased as well and this is becoming a lot more competitive than expected.

Therefore, I don't think that investing in a mining rig would be profitable in the current scenario.