I would like to have some university students design something for me and instead of payment, I like the idea of listing them on the patent with myself, for their resume)but they will have no ownership or rights to the product whatsoever. Is this a common practice? Would the patent be weaker? Thanks. Or is it better to pay them and not be on the patent?

Sounds like you need to talk to a patent attorney.

Sounds like you'll need some kind of agreement with these grad students, saying they get to take the credit for the patent but can't get any of the money the patent may earn.

Me?  I might be willing to work for free so long as I'm able to reap the rewards of the patent, but it'd be a big hell no to work for free, get my name listed on a patent, and then not be able to get paid if the patent is worth anything.  Pay me now, or pay me later, but you're gonna pay me.

You want smart people to work for you for free just so they can have their name(s) on a nice piece of paper with a little ribbon printed in a government office?
I assume you're not a professor at a university. If you are I feel bad for your students, and you should go talk to your university's in-house patent people.
If you have an idea for an invention you should talk to a patent lawyer about getting an application drafted and filed.

Under U.S. law you're an inventor or you aren't. There's no "people we named because they helped out in the lab" provision.
If you need smart people to work out the details of making your idea a possibility your a patent lawyer can help you to protect your idea and determine who is and who is not an inventor if your group comes up with something.

I have to agree here... smart people work hard to get where they are. If you truly need them they deserve to get something from it... either payment up-front for their work or payment on the back-end.

You might find a sucker that wants a resume booster but I doubt it...

FWIW, I'm an engineer, went to one of the top schools in the nation. My college has a separate legal entity that employs students on research projects for industry. They've succeeded in numerous patents on things (especially in the biomed field). All those patents belong to the industry partners that hired them though...because they were hired... their skills were needed, but the industry partner bought those skills to complete his/her/their patent.

When I was in school the going rate for a summer intern, doing said research & develop for industry partners was $13-18/hr. I think you would be able to very easily hire your own interns if you were willing to pay a similar rate...

The only other option I can think of is to have it as a class project. It's not unusual for class projects in engineering/science degree programs to be legit projects for local businesses etc. My senior design project was for a local company that made mining cutters/chains/etc to go on very large equipment. We did that work completely free. But the catch is, #1 the details of your idea may not be kept confidential if done through a class project, you can have them sign NDA's, but they will have to share details with the professor and possibly other students. #2 I have no idea how patent law is involved and who maintains patent rights if something patentable is created.

NotUrLawyer is correct.  For a person to be named as an inventor, such person must contributed to the invention that is claimed.  Your patent attorney should be able to assist you with this.