First, just ask the lady if she offers role-play. This is an innocent enough question which I think many ladies will answer.
If yes, and she doesn't respond by asking you what it is you have in mind, then follow up by asking if you may tell her the role-play scenario you want. Unless she gives the go-ahead, do not get graphic.
Or, if there's no way to tell her what you want WITHOUT explicit language you might want to try writing it as something that happened to you in the past.... or in the form of a fictional short-story. You can find erotic stories easily enough, if you're not possessed of creative-writing skills.
Definitely ask about role-play in advance. True story: a client did not ask me anything about role-play prior to meeting, but waited to do so until we were together. Now, I don't do role-play so I should have just said no but I was curious what he had in mind so I asked him that. And he leaped forward, knocking me down, pinning me to the bed and replied, "THIS! Is this ok?"
Yeah, he wanted what I have since learned is a consensual/non-consensual (i.e. rape fantasy) scenario.
It didn't go so well for him.
So ask first.
xoxoxoxoxo