It's not advisable to build a mining rig right now, GPUS are out of stock in every store in my country and that's not the worst part, I bought my gtx1660 ti for 400$ each and today it's 640$, the fact is people even still don't mind buying this cards at 640$ each, are they stupid? I don't know but getting back ROI should be their most worries, I think it's now nothing but FOMO