put all costs on the paper first.

1. power price  kWh  ( let says 0.13 usd kWh)
2. gpu costs...   let says nvidia gtx1070  350eur each
3. CPU + mobo + hdd + ram + PSU


put info in mining calculator like whattomine.com...  6 gtx1070 can get around 180mh/s   so with this prices its $6.5  per days,  of $4.5  with power cost  because it will draw around 700W.

so rough  around 3000USD you need to build 6x gtx1070 + mobo etc.

in best  case scenatio you will earn $1500 per year so you need like 2 years to pay out this equpement.   and this prices sis for used items, new are more more expensive.