If your 1080ti is only making $1 a day you are doing something wrong. I know people running a single 1080ti and they are making $3-$5 per day. Where are you getting your information or what are you mining and on what settings? That $3-$5 per day figure is without running the card intense, unless you consider 65c and 76% TDP to be anything except conservative.
You're doing something wrong if your goal is primarily to make the most $ per day. Maybe we can help you figure it out and optimize.
Are you sure you're not quoting prices from a few weeks ago? Bc mining seems to have really taken a hit in the past few weeks, ASICs and GPU alike. Currently a 1080ti is only making around $1.86 or so and thats not subtracting energy costs. This is without overclocking, but still significantly lower than what it was even 2 months ago (they were making $10-12/day easy). I'd ask your friend when you can to make sure he's still making $3-5/day bc to my knowledge I don't see how that's possible regardless of what alt you're mining at the moment.