Without complete requirements analysis, there can be no design. It's just a guess if you don't have firm requirements in both function and performance.

When they say, "That doesn't matter, it just has to work" you should close your briefcase and walk away.

If they haven't developed their requirements yet, you can't develop a solution, because they don't know what the problem is.

If they can't tell you what the job is, how can you determine whether you can do it? How can you know when you've finished? How can you determine when you'll get paid? How can you define acceptance test criteria if they haven't given you a set of requirements that you have to meet?

When you start a job, you have to have two things. (1) a set of definitive specifications for the completed task, and (2) a retainer in the bank to cover your cost while getting there. Absent those two things, there's no job.

RE